Soft, fluffy sourdough brioche donut balls with a rich buttery crumb and a melted chocolate center. These baked donut balls are lightly sweet, beautifully golden, and finished with a buttery sugar coating, just like bakery-style brioche donuts but made at home with natural sourdough fermentation.
In a large bowl, mix the sourdough starter, milk, eggs, sugar, and salt until fully combined.
Add the flour and mix until a rough dough forms.
Knead the dough until it begins to smooth, then gradually add the softened butter a little at a time, kneading until fully incorporated and the dough is elastic and glossy.
Cover the dough and let it rest at room temperature until slightly puffy, about 3-4 hours. Transfer the dough to the refrigerator and cold ferment overnight for 12-14 hours.
Remove the dough from the fridge and divide it into 10 equal pieces.
Flatten each piece slightly, place a chocolate square in the center, pinch the dough closed tightly, and roll into a smooth ball.
Place the dough balls seam-side down on a parchment-lined baking tray.
Cover loosely and let rise at room temperature until noticeably puffy, about 2-3 hours.
Preheat the oven to 180°C (350°F).
Bake for 18-20 minutes, until golden brown on top. Brush the warm donut balls generously with melted butter.
Roll each donut ball in granulated sugar or cinnamon sugar until evenly coated.