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rainbow cake with german buttercream recipe — sky-girl’s fifth birthday!

five, for the last time ::::

One month ago: “Mommy, I want a Paw Patrol birthday cake. Maybe with Skye cookies!”

“Ok.” [I start planning. I peruse Pinterest. I study frosting recipes. I look at cookie cutters shaped like dog biscuits.]

Three weeks ago: “Mommy, I want a cake with rainbows.”

“Um, ok. No Paw Patrol?”

“No, I changed my mind.”

“Ok, I’ll start getting rainbow supplies.” [Changes tack. Reviews Pinterest again. Orders new gel colors and tylose. Checks fondant supply. Throws away unsalvageable two-year-old gum paste.]

“Ok!” A cheery response from a cheery girl.

Two weeks ago: “I’m going to have a unicorn birthday with cupcakes, Mommy.”


Peach approaches me soon after. “Mommy, Sky said that I can make unicorn cupcakes for her birthday. How do you make unicorn cupcakes? I want to make unicorn cupcakes.”

“Wait, I thought she wanted rainbows?” Peach actually had rainbows at her fifth birthday, too.

[Eye roll from the tweenager.]

I made the rainbow cake. Peach made cupcakes with pink icing and gum paste stars. Nobody cared about unicorns after the big reveal of the cake and cupcakes dripping with icing.

And that is often how Sky-Girl is. Reveling in the fun of now. We had a small birthday party with friends. There were enough kids to keep her busy running around at the indoor play park, bouncing from one friend to another effortlessly. It was a mad rush to each apparatus to test each out: Let’s spin on the mini merry-go-round. I’ll climb up the bungee cord layered tower without bonking someone below me. Let’s dance on the pressure sensitive floor lights, watching the colored lights follow our steps.

At this facility, there is always a choice for the birthday party option to include the child’s dance with a “mascot.” These mascots are popular Disney characters usually and Sky-Girl chose Elsa. “Mascot” is a more than appropriate name. Sky-Girl got exactly that: a silent, tall, and comically large mascot-headed person dancing with her on this lit up dance floor with disco lighting. It was as if the mascot at the local farm league football game got sidetracked and stopped in for a creepy dance. Sky humored her. But sweetly declined a one-on-one photo op with the buffoony Elsa.

For her birthday dinner later, she requested Chick-Fil-A so that her siblings could get something they liked (not so much for the parents). They dove into milkshakes afterwards, stomachs already heavy with chicken bits and waffle fries. The kids headed to the play structure enclosed in the restaurant as Eat and I watched them bound off, Sky-Girl perky and ready as a kid just up from a fat nap. And we were condensed with love in the midst of the kids’ bounciness.

It is the now that is more condensed, more full, as I realize this is the last fifth birthday we will celebrate with one of our children. When Sky-Girl was first born, she was minutes old. One minute felt like a century. Then she was one year old and two months; a minute felt smaller. Then three years old and a week. Each minute that passes is smaller in the infinite sum of her. So be it that she pack in as much as she can into each and that I do the same.

She reaches for hugs at bedtime and goodbyes, and if the hug isn’t up to snuff, we have to do it over again. More minutes of hugs, more hugs in the infinite sum of her.

I love you, Sky. Have a great fifth year making the minutes count.


Here is a quick primer on how to form the gum paste for the topper. The German buttercream frosting recipe is below. My ingredients for the rainbow topper:

White fondant, tylose powder, Americolor gel colors, a 2-inch diameter biscuit cutter for shaping, 2 lollipop sticks, 2 toothpicks, and a large pan lined with parchment or silicone mat. Allow at LEAST three days to assemble the rainbow. It needs to have time to dry, especially if you live in a humid climate.

Tint your fondant or buy the already-colored. Mix a little tylose powder into each bit (a sprinkle is all I needed for small handfuls of fondant). Alternatively, you can buy gum paste instead and form into the shapes (which is essentially fondant + tylose powder already mixed). The tylose helps stabilize the fondant. It dries very hard and withstands humidity better. Shape the snakes of fondant around a 2-inch biscuit cutter. Stick them together with a little water or a glue made from a little water and a sprinkle of tylose powder. Make sure you adjust the size of your topper depending on what diameter you plan to make the cake. My topper ended up being about 7-inches across, fitting just perfectly on top of the 7-inch diameter cake top layer.

Next, trim straight across using a ruler. Once cut, add the toothpicks and/or lollipop sticks into the middle of the green and orange strips. Allow to dry for at least overnight.

Now roll white fondant on a clean mat with a little tylose and form into pea- to marble-shaped balls. Stick these together onto the rainbow using water or tylose glue. Allow this to dry overnight again. I used an aspic cutter to make stars with the leftover bits of colored fondant. We ended up not using them on the cake — though there was serious discussion from the kids about needing stars on the cake. Some of them ended up on the pink cupcakes.


“I love the rainbow, Mommy!”

At the end of the party, when we were home, the rainbow was deftly deconstructed and eaten with calm focus. Grub drooled nearby, and Sky-Girl, realizing how dense and sugary the rainbow was after gnawing on it, allowed him to snap off a few pieces to do the same. Peach ended up with a side of bright clouds.

I love you, babe. Have a wonderful fifth year.


One year ago: bourbon cherries (My prep for our trip to Japan. We celebrated Sky-Girl’s fourth birthday at Mount Fuji.)

Two years ago: minnie mouse cake roll (for her third birthday)

Three years ago: hello kitty cake roll (the second birthday!)

Three and a half years ago: We celebrated Sky-Girl’s first birthday realllllly late, and it also coincided with the blog’s fourth anniversary: pandan chiffon cake

Four years ago: goodbye, california!

Five years ago: mummy’s fudgy chocolate oatmeal bars recipe – and our new arrival (the birth of Sky-Girl)

Six years ago: thai iced tea and butterfly purple ombre cake

Seven years ago: cranberries all around and honeyed goat cheese tart

rainbow cake with german buttercream recipe -- sky-girl's fifth birthday!
Recipe type: Dessert
Prep time: 
Cook time: 
Total time: 
This recipe is actually just for the buttercream. For the rainbow topper, follow the instructions and photos in the post. The tutorial I followed was from Choose whatever cake recipe you prefer. Lemon or vanilla are great. I used two 8-inch rounds and one 7-inch round. I had plenty to fill and cover the cake and about 2-3 cups leftover.
  • 16 ounces whole milk
  • 1 teaspoon vanilla extract
  • 1 teaspoon lemon extract
  • 1½ cups sugar
  • ⅓ cup cornstarch
  • 2 eggs
  • 2 egg yolks
  • 16 ounces unsalted butter, softened
  • 16 ounces mascarpone cheese, room temperature
  • ½ teaspoon salt
  • juice of one small lemon
  1. Simmer milk in a sauce pan.
  2. Whisk the cornstarch, sugar, yolks, and eggs in a mixing bowl. Once the milk simmers, whisk a ladle of the hot milk into the eggs. Do one ladle at a time, whisking constantly, to temper the eggs. You do NOT want scrambled eggs. After about half the milk is added, then pour the entire mix back into the pot and continue to cook. Cook this mixture stirring constantly at a simmer until thick and bubbles slowly like hot lava. Cook for a full minute to fully cook the cornstarch.
  3. Remove from heat and transfer to a large mixing bowl. Cool in fridge with plastic wrap on top to prevent skin from forming OR cool while mixing at medium speed in a stand mixer. The pastry cream must be completely cooled before proceeding to next step. If it is warm at all, the butter and mascarpone will melt when you add them. If you chill in the fridge and the mixture is cold, then beat for a few minutes on medium until creamy before proceeding.
  4. Now, add the very soft butter one tablespoon at a time. Then do the same with the mascarpone.
  5. Add the lemon juice and salt and whip until smooth and creamy.
  6. Use the buttercream right away, or refrigerate or freeze. Bring to room temperature and whip until fluffy before using.
  7. If the buttercream breaks (curdly mess!), look at my buttercream post on how to fix it.
  8. Frost the cake with crumb coat, chill, then add thicker coat. I frosted the night before and chilled (this is not a buttercream you can leave at room temperature for a day or two).
  9. ADD THE RAINBOW: I chilled the cake a little before I added the rainbow to make sure it could withstand the weight. Before putting it into the cake, measure the height of the cake and the length of the lollipop sticks. Trim if needed.


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