Prep the pan and oven. Preheat the oven to 425°F. Line a 12-cup muffin pan with liners and lightly grease the top of the pan to help prevent oversized muffin tops from sticking.

Combine the dry ingredients. In a large bowl, whisk together the flour, baking powder, baking soda, salt, and sugar.

Combine the wet ingredients. In a separate bowl, whisk the sourdough discard, sour cream, oil, milk, eggs, and vanilla until smooth.

Make the batter. Pour the wet ingredients into the dry ingredients. Fold gently with a spatula just until a few streaks of flour remain. Add the chocolate chips and fold only until evenly distributed. The batter should be thick and scoopable, not pourable.

Rest and fill. Let the batter rest for 15 minutes. Divide it between the muffin cups, filling them very full, about 90–100 g batter per cup or roughly two 3-tablespoon scoops. Add a few extra chocolate chips and a sprinkle of coarse sugar to each top.

Bake. Bake at 425°F for 5 minutes. Without opening the oven, lower the temperature to 350°F and bake for another 12–15 minutes, until the tops are tall and golden and a toothpick inserted into the center comes out with a few moist crumbs.

Cool. Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack.