In a large mixing bowl, whisk together the all-purpose flour, cocoa powder, and powdered sugar.

Add the chilled, cubed butter to the flour mixture. Use a pastry cutter or your fingers to blend until the mixture resembles coarse crumbs.

Add the egg yolk and mix until combined. Gradually add cold water, one tablespoon at a time, mixing until the dough comes together.

Shape the dough into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

Preheat the oven to 350°F (175°C).

Roll out the chilled dough on a lightly floured surface to fit your tart pan. Carefully transfer the dough to the pan, pressing it into the edges.

Prick the bottom of the crust with a fork to prevent bubbling. Bake for 15-20 minutes or until firm. Remove from the oven and let cool.

In a medium saucepan over medium heat, melt the granulated sugar, stirring constantly until it turns a deep amber color.

Once melted, carefully add the cubed butter and stir until melted and smooth.

Slowly pour in the heavy cream while continuing to stir (the mixture will bubble up). Add the sea salt and mix until fully combined. Remove from heat and let cool slightly.

Pour the cooled salted caramel filling into the baked tart crust, spreading it evenly.

Allow the tart to cool completely at room temperature, then refrigerate for at least 2 hours to set.

Before serving, sprinkle flaky sea salt over the top for garnish. Optionally, add dollops of whipped cream or chocolate shavings.

Slice and enjoy your delicious salted caramel tart!