Author: story of a kitchen (from http://theimprovkitchen.blogspot.co.uk/2012/05/some-foods-just-go-together.html?m=1)
Recipe type: dessert
Ingredients
FOR THE CRUST: 9 tablespoons unsalted butter
¼ cup sugar
1 cup flour
1 teaspoon vanilla extract
pinch of salt
FOR THE FILLING: 12 ounces frozen raspberries, thawed, and/or fresh raspberries
¾ cup sugar
⅔ cup fresh lemon juice
2 tablespoons lemon zest
3 egg whites
1 egg
⅔ cup flour, sifted *
pinch of salt
powdered sugar for dusting, optional
Instructions
Preheat oven to 350 degrees F.
Line an 8x8-inch baking pan with parchment paper (no need to butter). Make sure your edges overhang enough that you can use them to remove the baked, cooled uncut bar from the pan to cut more easily.
MAKE THE CRUST: Cream the butter and sugar together with an electric mixer, then add vanilla. Add flour and mix until just incorporated. Dump dough into prepared pan and press until evenly covering bottom of the dish. Bake for 20 to 25 minutes until slightly golden brown.
MAKE THE FILLING: Put the berries in a fine mesh sieve and press to recover solids and extract juice into a large bowl. If you don't mind seeds, you can add them in whole.**
Add sugar, egg whites, egg, lemon juice, zest, flour, and salt to the bowl and stir to combine. Pour the mixture into the crust and bake for 25 to 30 minutes. First check your raspberry lemonade bars at 25 minutes and then again in about three more minutes until you see that the center has set. You are looking for a matte finish across the top, without over baking the edges. Overbake and you'll end up with rubbery edges. (Which are easily trimmed and eaten....no one has to know.)
Allow to cool to room temperature and then place in the refrigerator for a few hours to cool completely. I couldn't wait that long, cutting into them after about two hours in the fridge. I was not disappointed.
I imagine these would do well with just about any berry as a substitute. Other variations I've dreamed about are black tea and lemon, guava and lime.