Soak the oats: In a bowl, combine the rolled oats and milk. Let sit for 10–15 minutes until the oats look plump. This step softens the oats and prevents a dry crumb.

Prep your pans and oven: Heat the oven to 400°F (200°C). Line a 12-cup muffin pan with liners or lightly grease the cups.

Mix the dry ingredients: In a large bowl, whisk the flour, baking powder, baking soda, and salt until well combined. Whisk in the granulated and brown sugar to break up any clumps.

Combine the wet ingredients: In a separate bowl, whisk the eggs, oil, yogurt (or buttermilk), vanilla, and the soaked oats with their milk.

Bring it together: Pour the wet mixture into the dry ingredients. Stir gently with a spatula just until you no longer see dry flour. The batter should be thick and slightly lumpy. Do not overmix.

Fold in the blueberries: Add the blueberries and fold carefully to distribute. If using frozen berries, keep them frozen to reduce streaking and excess moisture.

Fill the cups: Divide the batter evenly among the muffin cups, filling each about 3/4 full. For a bakery-style top, you can fill a bit higher. Sprinkle with coarse sugar if using.

Bake: Place the pan on the center rack. Bake for 5 minutes at 400°F (200°C), then reduce the temperature to 375°F (190°C) and bake another 12–15 minutes, until the tops are set and a toothpick comes out clean or with a few moist crumbs.

Cool: Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack. They’ll firm up as they cool and release more easily from the liners.

Serve: Enjoy warm or at room temperature. A swipe of butter or a drizzle of honey is a nice touch.