Preheat the oven to 350°F (180°C) and line a baking sheet with parchment paper. Have your pastry ring ready.

In a bowl, combine the flour, icing sugar, cocoa powder, and salt for the tart base.

Add the melted butter and vanilla, then mix until you get a smooth, thick paste.

Knead the dough briefly and flatten it into a circle larger than your pastry ring.

Bake the tart base for 10 minutes until dry and set.

Immediately press the pastry ring into the hot pastry and let it cool.

In a bowl, whisk the egg yolks, whole eggs, and sugar together.

Whisk in the cornstarch and salt until smooth.

In a saucepan, heat the milk and cream until steaming. Slowly add to the egg mixture to temper.

Return mixture to the saucepan and cook, whisking continuously until thick and bubbling.

Remove from heat, strain if necessary, and stir in the chopped dark chocolate until melted and smooth.

Pour the custard into the cooled tart base still in the ring.

Bake for 50-60 minutes until the edges are set and the center jiggles.

Let cool to room temperature, cover and refrigerate overnight.

Remove the ring and glaze with warmed jam before serving.