Blackberry Lemonade Bars with Hazelnut Shortbread Crust
for the crust
1 c. whole hazelnuts, toasted and skinned
1/4 c. sugar
1 1/4 c. flour
1/4 tsp. salt
13 Tbsp. (1 1/2 sticks plus 1 tablespoon) unsalted butter, chilled and cut into 1/2-inch cubes
for the filling
3 c. sugar
1 1/3 c. flour
3 Tbsp. lemon zest
1/4 tsp. salt
3/4 c. strained blackberry puree
6 egg whites
1 1/3 c. freshly squeezed lemon juice
powdered sugar, for dusting
Make the crust first. Preheat oven to 350º. In the bowl of your food processor, combine hazelnuts and sugar, process until nuts are finely chopped. Add in flour and salt and process for 5 seconds or so to combine. Add butter and process until dough comes together, pulling away from the sides of the bowl. Press into parchment-lined 13" x 9" baking dish, being sure to make it an even thickness throughout. Bake for 22-23 minutes.
While the crust is baking, assemble the filling. Combine four, sugar, and salt in a large bowl, whisking to blend. In a separate bowl, combine the lemon juice, lemon zest, and blackberry puree. Add the eggs and egg whites to the dry ingredients and whisk to combine. Then whisk in the lemon juice mixture until smooth.
When the crust has been pre-baked, immediately pour filling over top and place back in the oven and bake until center is just set and no longer jiggles when shaken; 35 - 40 minutes. Let cool to room temp, then chill well (for at least two hours).
When you're ready to serve them, carefully tug up the parchment, pulling out the bars in one big piece. (You may want to gently loosen any areas not contained by the parchment with a butter knife.) Place on a cutting board or mat, and slice into squares. Dust with powdered sugar.