Dough
1/2 cup (120 ml) milk, preferably whole
1/4 cup (50 grams) plus a pinch of granulated sugar
1 1/2 teaspoons (5 grams) active dry yeast
1 large egg, brought to room temperature
2 cups (250 grams) all-purpose flour, plus more for work surface
1/2 teaspoon table salt
3 tablespoons (45 grams) unsalted butter, at room temperature, plus additional for bowl and muffin tins

Filling
3 tablespoons (45 grams) unsalted butter, at room temperature
1/4 cup (50 grams) granulated sugar
1/2 pound (225 grams) semisweet chocolate
Pinch of salt
3/4 teaspoon ground cinnamon (optional)

Egg wash (optional)
1 egg
2 teaspoons (10 ml) heavy cream or milk