For topping:1 cup 35% whipping cream2 tablespoon sugarFor the pastry, beat the butter and icing sugar and salt until smooth and creamy and then mix in the egg yolks all at once until well combined. Sift the flour and cocoa over the mixture and stir until evenly combined to form a stiff dough. Shape the dough into a disc, wrap with plastic and refrigerate for 1 hour.

Preheat the oven to 350 degrees F.

Have ready an ungreased 12-cup muffin pans.Let the dough rest at room temperature for 10 minutes to soften slightly before rolling. Roll the dough between two pieces of parchment paper to a circle just less than ¼-inch thick. Using a 4-inch round cutter, stamp out as many circles as you can. Fit each round into the well of a standard 12-cup muffin pan, pressing it into the bottom and up the sides. Re-roll the scraps of pastry and cut out more circles as necessary. Chill for 15 minutes.

Dock each pastry with a fork and bake for 10-12 minutes, until dry and crisp. Transfer pan to wire rack to cool and reduce oven temperature to 300 degrees F.

Meanwhile, to make the chocolate filling heat cream in a saucepan until it comes to a boil. Add chopped chocolate and let stand for 2 minutes before whisking gently until smooth. Let cool for 5 minutes and then stir in sugar, egg and salt until well combined. Spoon filling into pre-baked tart shells and bake for 10-14 minutes, until just set around the edges but very slightly soft in the middle. Transfer pan to a wire rack to cool completely. Refrigerate if not serving right away.

When ready to serve, whip cream until thickened and then sprinkle in sugar and continue whipping until it holds soft peaks. Pipe cream around the edges of the tarts and serve.