Preheat your oven to 350°F (175°C) and line your muffin tin with cupcake liners.
Divide the dough into 20 equal pieces. Take a little more than half of each piece of dough and transfer it into the liner, spreading it out with your hands, forming a mini tart shape (like a nest). Fill with a heaped tablespoon of filling and crumble on top the rest of the piece of dough with your fingers. Continue with the rest of the muffins.
If you have any filling left, store it in the fridge. You can let it come to room temperature and slather it on bread.
If you want to make half the recipe, use 1 egg yolk and 1 tablespoon egg white