Blackberry Mascarpone Tart with Thyme Shortbread Crust

Beat butter in a large bowl with an electric mixer until creamy. Add 1/4 cup confectioners' sugar and 1/2 teaspoon vanilla extract; beat to combine. Add egg; beat until incorporated. Gradually beat in flour, thyme, and salt until dough comes together and pulls away from the sides of the bowl. Knead dough slightly; shape into a ball. Wrap in plastic wrap; refrigerate for 30 minutes.

Preheat the oven to 375 degrees F (190 degrees C). Grease a 9-inch round or 13x4-inch rectangular tart pan with a removable bottom.

Press dough evenly into the prepared tart pan.

Bake in the preheated oven until lightly browned, 12 to 14 minutes. Cool completely before filling, about 30 minutes.

Combine 1/2 blackberries and 1/2 tablespoon white sugar in a small saucepan over medium-low heat; cook and stir, crushing berries with a spoon, 4 to 5 minutes. Press mixture through a fine-mesh sieve; discard solids. Return crushed berries to the saucepan.

Combine cornstarch and cold water in a small bowl; add to the crushed berries and cook over medium heat until comes to a boil and starts to thicken, 3 to 5 minutes. Cool.

Beat mascarpone cheese, 3/4 cup confectioners' sugar, and 1 teaspoon vanilla extract in a bowl with an electric mixer until smooth.

Beat cream in a chilled glass or metal bowl with an electric mixer until frothy. Add 1 tablespoon white sugar gradually, continuing to beat until stiff peaks form. Fold whipped cream into mascarpone mixture; mix well. Spread filling evenly into the cooled crust. Drop teaspoonfuls blackberry sauce on top of filling; gently cut through sauce and filling using a knife to swirl. Garnish top of tart with remaining 1/2 blackberries and mint.