Follow these steps for perfectly baked, delicious muffins every time:

1. Preheat and Prep: Preheat your oven to 400°F (200°C). Line a 12-cup standard muffin tin with paper liners or grease it well with butter or cooking spray.
2. Combine Dry Ingredients: In a large mixing bowl, whisk together the all-purpose flour, rolled oats, packed light brown sugar, baking powder, baking soda, ground cinnamon (if using), and salt. Make sure there are no lumps of brown sugar.
3. Toss Blueberries (Optional but Recommended): If using fresh blueberries, gently toss them with 1 tablespoon of the dry flour mixture. This helps prevent them from sinking to the bottom of the muffins during baking. If using frozen blueberries, skip this step and add them directly to the batter at the end, ensuring they are not thawed.
4. Combine Wet Ingredients: In a separate medium mixing bowl, whisk together the lightly beaten egg, plain yogurt (or buttermilk), vegetable oil (or melted coconut oil), and vanilla extract until well combined.
5. Combine Wet and Dry: Pour the wet ingredients into the dry ingredients. Using a spatula or wooden spoon, mix just until combined. It’s crucial not to overmix the batter; a few lumps are perfectly fine. Overmixing develops gluten, which can lead to tough muffins.
6. Fold in Blueberries: Gently fold the blueberries into the batter. If using frozen blueberries, work quickly to prevent them from thawing and bleeding too much color into the batter.
7. Fill Muffin Cups: Divide the batter evenly among the 12 prepared muffin cups, filling each about two-thirds to three-quarters full. An ice cream scoop can be helpful for even distribution.
8. Optional Topping: For an extra touch, you can sprinkle a little extra rolled oats or a pinch of granulated sugar on top of each muffin before baking.
9. Bake: Bake in the preheated oven for 18-22 minutes, or until the tops are golden brown and a wooden skewer or toothpick inserted into the center of a muffin comes out clean (a few moist crumbs are okay, but no wet batter).
10. Cool: Let the muffins cool in the tin for 5-10 minutes before carefully transferring them to a wire rack to cool completely. This prevents them from becoming soggy on the bottom.