Preheat the oven to 375℉/190℃ and line a muffin tin with liners (8 tulip OR 12 regular) and set aside. Zest 1 lemon for later.
Lemon zest from 1 lemon
In a bowl, add the flour, oats, baking soda, baking powder, cornstarch, and salt. Stir to combine and set aside.
1 1/2 cups all-purpose flour, 1 cup rolled oats, 1 1/2 tsps baking powder, 1 tsp baking soda, 1/4 tsp salt, 1 tbsp cornstarch
In a large bowl, add the lemon zest and white sugar. With your fingers, rub together and combine them for about a minute to release the lemon oils and fragrances.
3/4 cups white sugar, Lemon zest from 1 lemon
Add in the eggs, vanilla, oil, and buttermilk, Whisk together until well combined.
1 cup buttermilk*, 1/2 cup oil, 2 large eggs, 1 tbsp vanilla
Combine the dry and wet ingredients together gently with a spatula until almost completely combined. Then add in the raspberries and mix a few more times until combined. Don’t over-mix!
1 1/2 cups raspberries*
Scoop the batter evenly between the liners (about halfway full in tulip liners and all the way full in regular ones). Add extra raspberry pieces and sprinkle a bit of white sugar on top (optional).
Bake for 25-35 minutes or until a toothpick inserted in the middle comes out clean. I would start checking around the 20 minute mark. Mine took 30 minutes total.
Allow to cool, and enjoy! These muffins are such a hearty treat!