In a large mixing bowl, combine the egg and sugar. Beat until the mixture is light and frothy.
Add the vanilla yeast, oil, and soft butter. Mix well until combined.
Gradually add the flour and baking powder, stirring until a soft, pliable dough forms.
Knead the dough lightly on a floured surface. Cover with a clean cloth and let it rest for 15-20 minutes.
Step 2: Prepare the Chocolate Cream
In a medium saucepan, whisk together the egg, sugar, and cornstarch until smooth.
Gradually add the milk while whisking to prevent lumps.
Place the saucepan over medium heat, stirring constantly until the mixture thickens.
Remove from heat and stir in the dark chocolate until melted and smooth.
Let the mixture cool slightly, then gently fold in the sweetened cream until well combined.
Step 3: Assemble the Tart
Preheat your oven to 180°C (350°F).
Roll out the dough on a floured surface to fit your tart pan. Transfer the dough to the pan, pressing it evenly into the bottom and sides. Trim any excess dough.
Prick the base of the dough with a fork to prevent puffing during baking.
Bake the crust for 15-18 minutes, or until golden brown. Let it cool completely.
Step 4: Add the Chocolate Cream
Once the crust has cooled, pour the prepared chocolate cream into the crust, spreading it evenly.
Sprinkle chocolate chips on top as desired.
Step 5: Chill and Serve
Refrigerate the tart for at least 2 hours to allow the chocolate cream to set.
Before serving, dust with powdered sugar for an elegant finish.