Preheat the oven to 425℉/218℃. Line the muffin tin with 12 liners and set aside.
In a bowl, add the dry ingredients. Mix together and then set aside.
1 1/2 cups all-purpose flour, 1 1/4 cups rolled oats, 1 tsp baking soda, 1 1/2 tsps baking powder, 1 tbsp cornstarch, 1/4 tsp salt
In a large bowl, add the lemon zest and brown sugar. Using your fingers, mix them together for about a minute.
1 tbsp lemon zest, 3/4 cups light brown sugar
In the same bowl add the wet ingredients. Whisk for 2-3 minutes until well mixed.
1/2 cup oil, 1 cup full-fat sour cream, 3 tbsp lemon juice, 2 large eggs, 1 tbsp vanilla
With a spatula, mix together the dry and wet ingredients together. Gently mix until just combined. As soon as there are no more flour streaks, stop mixing.
In a medium-sized bowl, add the washed blueberries and 1 tbsp of flour. Mix around until the berries are evenly coated in flour. This will help them not sink as they bake. Then add them into the batter and mix a few times. Do not over-mix!
1 1/2 cups fresh blueberries
Fill the muffin liners to almost the top. This recipe makes 12-14 regular-sized muffins depending on how full you fill them. Add extra blueberries and sprinkle a bit of white sugar on top (optional).
Bake the muffins at 425℉ for 5 minutes, then lower the temperature to 375℉ and continue baking for another 15-18 minutes or until a toothpick inserted comes out clean.