Making the crust dough. In the bowl of a food processor, combine butter and sugars. Blend until smooth. Add beaten eggs and vanilla extract until combined. Scrape down the sides of the bowl as needed with a rubber spatula. Add in flour and salt and pulse until dough form. Turn out onto a sheet of plastic wrap, form into a disc, wrap and chill for 30 minutes. 226 g unsalted butter, 150 g granulated sugar, 53 g light brown sugar, 1 teaspoon salt, 2 large eggs, 1 teaspoon vanilla extract, 510 g all-purpose flour
Blackberry filling. While dough is chilling, mix together all blackberry filling ingredients. Mash any larger berries with a fork, but keep mostly intact. Place in a sieve above a bowl to catch any juice. Set aside.
680 g 24 ounces fresh or frozen blackberries (thawed if frozen), 150 g granulated sugar, 1 1/2 teaspoons cinnamon, 3/4 teaspoon ground nutmeg, Zest of 1 lemon, 1 1/2 teaspoons fresh lemon juice, 3 tablespoons cornstarch
Making the crust shells. Preheat oven to 350°F. Once dough is chilled, divide the dough in two. Rewrap one half and place back in the fridge. Roll the other half out on a floured surface to a 1/8" layer. Cut 6 circles wider than your individual tart pans. Using your thumb, press the dough into the corners and up the sides of the pans. Using a sharp knife, trim away any excess on the edges. Repeat for each tart pan. Using a fork, pierce the bottom of the dough 10+ times to allow steam to escape. Place the tart pans on a sheet tray, cover lightly with plastic wrap, and chill for 15 minutes. Once chilled, place sheet pan in oven and bake for 12 minutes. Remove and allow to cool to the touch.
Making the lattice. While shells are baking, unwrap the second half of the dough, roll on a floured surface 1/8" thick. Cut 1/2" wide strips about 6" long.
Making the finished tarts. Once the pre-baked shells are cool to the touch, fill with 1/2 cup of blackberry filling, discarding any juice at the bottom. Place 3 strips horizontally across the top of the filling. Place 3 strips vertically, alternating weaving above and below the horizontal strips. With your thumb, press the strips into the bottom crust and pressing away any excess at the edge of the pan. Sprinkle the top with coarse sugar. Place sheet pan back in the oven, bake 35-40 minutes until filling is bubbling and lattice tops are browned.
Coarse sugar
Allow to cool to the touch before removing from tins. Serve as is or with vanilla ice cream or whipped cream if desired.