Ingredients For the Crust:
1 cup walnut pieces
1 cup all-purpose flour
1/2 cup confectioner sugar
1/2 teaspoon cinnamon
1/2 teaspoon salt
1/2 cup unsalted butter, softened and cut into tablespoon pieces
For the Blackberry Curd:
12 ounces (about 3 cups) fresh blackberries
1/2 cup water
1/2 cup granulated sugar
4 large eggs
4 large egg yolks
4 tablespoons lemon juice (from 1 lemon)
1/4 teaspoon salt
1/2 cup (4 ounces) unsalted butter, softened and cut into tablespoon pieces
For the Lemon Curd:
6 large eggs at room temperature
3 cups granulated sugar
2 tablespoons grated lemon zest (4 to 6 lemons)
1 cup freshly squeezed lemon juice
1 cup flour
Confectioners’ sugar, for dusting
Prepare the crust:
Line a 9×13 baking pan with parchment, as described in this tutorial.
Place the nuts in the bowl of a food processor and coarsely grind, about 15 one-second pulses. Add the flour, sugar, cinnamon, and salt, and pulse until finely ground, about 10 additional one-second pulses. Sprinkle the chunks of butter over the top of the flour-nut mix and pulse until the mixture holds together when compressed in your palm, another 20-25 one-second pulses. (See below for preparing the crust without a food processor.)
Press the crust mix into the baking dish, making it as even as possible. Freeze for 30-60 minutes.
Pre-heat the oven to 350°F. Remove the crust from the freezer and bake for 20-25 minutes, until beginning to color around the edges.
While the crust is baking, prepare the blackberry curd and lemon curd:
Place the blackberries and water in a medium-sized sauce pot over medium-high heat and stir. Continue cooking and stirring occasionally until all the blackberries have become mushy, about 5-8 minutes. Pour them into a fine-meshed strainer set over a medium-sized mixing bowl and press the berry puree through using a spatula. Allow the puree to cool to room temperature. Discard the berry skins and clean the strainer for use in the next step.
To the bowl with the blackberry puree, add the sugar, eggs and yolks, lemon juice and salt (reserving the butter for now). Stir thoroughly until the mixture is even.
Return the blackberry mixture to the saucepan and set the burner to medium. Stir the curd continuously, making sure to scrape the bottom and corners of the pan. Cook until the curd starts to thicken, coats the back of a spoon,This should take 10-12 minutes.
Remove the pan from the heat and add the butter all at once. Stir until the butter has completely melted, then pour the curd through the strainer into a clean bowl.
For the lemon curd, whisk the ingredients together in a medium size bowl.
Pour the lemon curd onto the walnut crust. Spoon the blackberry curd on top and swirl with a knife. Bake at 350° for 10-15 minutes, until the curd has set but still jiggles slightly in the center. Cool completely and refrigerate before cutting.
To cut the squares, lift them from the pan using the parchment paper as handles. Trim off the sides to make even edges if desired. Dust the tops of the bars with powdered sugar just before serving and use a sharp knife to cut them into squares. The powdered sugar will melt into the curd, making sweet glaze.
(Recipe adapted from cranberry curd bars and Lemon squares.)