Instructions:
Make the Chocolate Pastry:
In a food processor, pulse together the flour, cocoa powder, powdered sugar, and salt until combined.
Add the cold butter cubes and pulse until the mixture resembles coarse crumbs.
Add the egg yolk and pulse again until the dough starts to come together. If needed, add 1-2 tbsp of ice water, a little at a time, until the dough forms into a ball.
Flatten the dough into a disc, wrap in plastic wrap, and chill in the refrigerator for at least 30 minutes.
Prepare the Tart Shells:
Preheat your oven to 350°F (175°C).
On a lightly floured surface, roll out the chilled dough to about 1/8-inch thickness.
Cut out circles using a cookie cutter or glass that is slightly larger than your tart molds.
Press the dough circles into greased tart molds, trimming any excess dough. Prick the bottoms with a fork.
Place tart shells on a baking sheet and freeze for 15 minutes.
Bake the Tart Shells:
Bake the chilled tart shells in the preheated oven for 12-15 minutes, or until set.
Remove from the oven and let them cool completely in the tart molds on a wire rack.
Make the Salted Caramel Filling:
In a heavy-bottomed saucepan, heat the granulated sugar over medium heat. Stir constantly with a heat-resistant spatula or wooden spoon until the sugar melts and turns a deep amber color.
Carefully add the butter, piece by piece, stirring until melted and combined.
Slowly pour in the heavy cream while stirring constantly.