In a mixing bowl, combine 1 cup of all-purpose flour, ⅓ cup of icing sugar, ¼ cup of cocoa powder, and ¼ teaspoon of salt. Pour in 1 stick of melted butter and ½ teaspoon of vanilla extract. Mix until the dough forms a cohesive ball. Press the dough evenly into a tart pan and refrigerate for about 30 minutes.

In a separate bowl, whisk together 4 egg yolks and 2 whole eggs until well combined. Gradually add 1 cup of white sugar and ⅓ cup of cornstarch, mixing until smooth. In a saucepan over medium heat, warm 2 ½ cups of whole milk, 1 ¾ cups of heavy cream, and ½ teaspoon of salt until just before boiling. Slowly whisk the warm mixture into the egg mixture to temper the eggs.

Melt 7 ounces of dark chocolate in a microwave or a double boiler until smooth. Allow it to cool slightly before stirring it into the custard mixture until fully combined.

Preheat your oven to 350°F (175°C). Remove the tart base from the refrigerator and pour the creamy chocolate custard into it, smoothing the top with a spatula. Place the tart pan inside a larger baking dish filled with hot water. Bake for about 45-50 minutes until set but still has a slight wobble in the center.

Once baked, turn off the oven and let it cool in the water bath for about 30 minutes before removing and allowing it to cool to room temperature. Brush the top with 1 tablespoon of jam before refrigerating for at least 4 hours or overnight.

Slice into elegant pieces to serve. Pair with fresh berries or whipped cream for added flair.