Prep the pan and oven. Heat the oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or grease well. Starting hot helps the muffins rise tall and domed.

Combine dry ingredients. In a large bowl, whisk flour, baking powder, baking soda, and salt until evenly mixed. Set aside.

Whisk the wet base. In a separate bowl, whisk sugar, eggs, vanilla, and the melted butter until glossy. Whisk in the oil for extra softness.

Add dairy and discard. Whisk in the milk (or buttermilk) and the sourdough discard until smooth. It’s okay if you see a few tiny streaks from the discard; they’ll hydrate during the rest.

Bring it together. Pour the wet mixture into the dry bowl. Stir gently with a spatula until just combined. The batter should be thick and scoopable, not runny. Don’t overmix.

Fold in add-ins. If using chocolate, berries, or nuts, fold them in now. For blueberries, toss with a bit of flour first so they don’t sink.

Rest the batter. Let the bowl sit for 8–10 minutes on the counter. This short rest hydrates the flour and helps create a fluffy, bakery-style crumb.

Portion and top. Divide the batter evenly among the cups, filling each about 3/4 full. Sprinkle with coarse sugar if you like a crunchy top.

Bake high, then lower. Bake at 400°F (200°C) for 5 minutes to set the dome, then reduce to 350°F (175°C) and bake 12–15 minutes more, until the centers spring back and a toothpick comes out with a few moist crumbs.

Cool correctly. Cool in the pan for 5 minutes, then transfer to a rack. Don’t leave them in the pan too long or the sides can steam and turn rubbery.