Preheat oven to 375F/ 190C. Butter or spray with a non-stick baking spray an 8 or 9-inch square baking pan, then line with parchment paper so it comes up the sides slightly. (This will make it easier to remove the whole pan of bars for easier cutting.)

In a medium bowl, gently combine all the ingredients for the berry filling and set aside.

In the bowl of a food processor fitted with the blade attachment, add the flour, sugar, salt and cold butter and pulse until it resembles coarse crumbs. Then add the egg, vinegar, and vanilla and pulse a few more times until it just starts to come together. It should still be somewhat shaggy. If it's too dry add another teaspoon of vinegar.

Dump half of the dough mixture into the pan, and press down so it forms an even crust on the bottom of the pan. (The bottom of a glass cup can help with this.)

Then spread the one third cup of lemon curd evenly over the crust and spoon the berry mixture on top of the curd.

Evenly crumble the remaining half of the dough over the berries. (Leaving some of the dough in bigger chunks is not a bad thing.)

Place the pan in the refrigerator and chill about 15-20 minutes. (The freezer can be used to speed the process up.) Then place in the center of the preheated oven and bake about 40-45 minutes until the filling is bubbly and the crust is golden brown on top.

When finished baking, transfer the pan to a rack to cool. Then place the cooled pan in the refrigerator for about 30 minutes if desired for neater looking cut bars. (If you do this, you should be able to gently loosen the edges of the crust from the pan using a butter knife or offset spatula, then pull out the parchment tabs to release the whole pan of bars and cut as you wish.)