Make the Dough

1. In a large bowl, combine the flour, powdered sugar, salt, and lemon zest.

2. Cut in the cold butter until the mixture resembles coarse crumbs.

3. Add the egg, egg yolk, and vanilla bean paste. Mix just until the dough comes together.

4. Divide the dough into two portions: approximately two-thirds for the tart shell and one-third for the lattice.

5. Shape into discs, wrap well, and refrigerate for at least 1 hour or overnight.

Prepare the Tart Shell

1. Roll the larger portion of dough on a lightly floured surface until about ⅛ inch thick.

2. Carefully transfer to a tart pan and gently press into the bottom and sides.

3. Trim excess dough, leaving a slight overhang if desired.

4. Chill the tart shell for 10–15 minutes.

Prepare the filing*

Add both of the jams to a small saucepan.

Bring to a gentle simmer over medium heat.

Stir in the cornstarch and continue cookin for 3-5 minutes, stirring constantly, until the jam has thickened.

Remobe from the heat and allow to cool completely before filling the tart.

*If your jam is already quite thick, you may not need cornstach. I reduced my blackberry and blueberry james and added 1 tablespoon of cornstarch to create a thicker filling that would hold its shape and prevent the tart crust from becoming soggy.

Fill the Tart

1. Spread the blackberry jam evenly over the base.

2. If the jam is loose, refrigerate or freeze the tart for 15–20 minutes before adding the lattice.

Create the Lattice

1. Roll the remaining dough to about ⅛ inch thick.

2. Cut strips using a pastry wheel or knife.

3. Arrange strips diagonally across the tart.

4. Weave additional strips diagonally in the opposite direction to create a lattice pattern.

5. Trim the edges flush with the tart pan.

Chill

Place the assembled tart in the freezer or refrigerator for 15–20 minutes. This helps the lattice hold its shape during baking.

Bake

1. Preheat oven to 350°F (175°C).

2. Whisk together the egg yolk and milk or cream.

3. Brush the lattice and exposed pastry with egg wash.

4. Sprinkle lightly with turbinado or sanding sugar.

5. Bake for 35–45 minutes, or until the pastry is deep golden brown and the filling is gently bubbling.

Finish and Serve

1. Allow the crostata to cool completely before slicing.

2. Just before serving, dust lightly with powdered sugar.