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. Mix well until evenly blended. Then, add 1 stick of melted butter and ½ teaspoon of vanilla extract, stirring until a dough forms. Press this dough evenly into a tart pan and refrigerate for about 30 minutes to chill.

In a separate bowl, whisk together 3 egg yolks and 2 whole eggs until well combined. Over medium heat, whisk together 1 cup of white sugar, ⅓ cup of cornstarch, and ½ teaspoon of salt. Gradually stir in 2½ cups of whole milk and 1½ cups of heavy cream, heating until warmed but not boiling.

Remove the saucepan from heat and stir in 7 ounces of chopped dark chocolate until melted. Gradually incorporate the egg yolk mixture into the chocolate mixture, whisking continuously.

Preheat your oven to 350°F (175°C). Pour the chocolate custard mixture into the prepared tart shell. Bake for about 30-40 minutes, until the custard is set but slightly jiggly in the center. Allow to cool completely.

After cooling, cover the flan with plastic wrap and refrigerate for a minimum of 4 hours.

Before serving, gently heat 1 tablespoon of jam and brush it over the top of the chilled flan for a glossy finish.