In a mixing bowl, combine the flour, cocoa powder, and powdered sugar. Add the cold butter and mix until the mixture resembles coarse crumbs.

Add the egg yolk and ice water, mixing until the dough comes together. Press the dough into a 9-inch tart pan and refrigerate for 30 minutes.

Preheat the oven to 350°F (175°C). Line the crust with parchment paper and fill with pie weights. Bake for 15 minutes, then remove the weights and bake for an additional 10 minutes until set. Let cool.

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

Once melted, carefully add the butter and stir until melted. Slowly pour in the warm cream while stirring until combined. Remove from heat and stir in the sea salt.

Place the chopped dark chocolate in a bowl. In a saucepan, heat the heavy cream until just boiling, then pour it over the chocolate. Let sit for 5 minutes, then stir until smooth.

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

Pour the chocolate ganache over the caramel layer and smooth the top. Refrigerate for at least 2 hours to set.

Before serving, sprinkle with additional sea salt.