Combine the all-purpose flour, unsweetened cocoa powder, hazelnut flour, icing sugar, and salt in a mixing bowl.

Rub 125 g cold butter into the dry ingredients until the mixture resembles sand.

Add the medium egg and bring the dough together into a compact disc.

Roll the dough to a 3 mm thickness.

Line the 22 cm perforated tart ring with the rolled dough and trim the edges.

Freeze the lined tart shell for at least 60 minutes.

Bake the frozen tart shell at 160°C for 25 minutes.

Melt 160 g dark chocolate and stir in the vegetable oil.

Fold the chopped hazelnuts into the chocolate glaze.

Pour the glaze over the inverted baked tart shell and spread it evenly.

Refrigerate the glazed shell until the coating is firm.

Combine the pitted cherries, granulated sugar, and lemon juice in a saucepan.

Cook the cherry mixture over medium heat for 15 minutes.

Cool the cherry compote completely and spoon it into the tart shell.

Finely chop the remaining 200 g dark chocolate and place it in a mixing bowl.

Heat 200 ml heavy cream until boiling and pour it over the chopped chocolate.

Whisk the ganache smooth and incorporate 30 g cold butter.

Pour the ganache over the cold cherry compote and level the surface.

Refrigerate the tart until the ganache has set.

Mix the mascarpone, cream cheese, and remaining icing sugar until smooth.

Add 100 ml heavy cream and whip the mixture for 5 minutes.

Transfer the mascarpone cream to a silicone mold and freeze until solid.

Unmold the frozen mascarpone insert and place it on top of the tart.

Decorate the tart with fresh cherries before serving.