Preheat the oven to 350°F. Grease muffin cups with butter or non-stick cooking spray. Alternatively, fill each well with a muffin liner.
In a bowl of a stand mixer, beat the butter on medium speed until it's whipped and creamy, about 30 seconds. Then add the granulated sugar and beat together until light and fluffy, about another minute.
7 tbsp unsalted butter, ⅔ cup granulated sugar
Add the egg and vanilla to the mixture. Beat on medium speed until the mixture is pale and smooth.
1 egg, 1 tsp vanilla extract
In another bowl, whisk together the flour, baking powder, baking soda, cinnamon and salt.
1½ cups all-purpose flour, 1½ tsp baking powder, ½ tsp baking soda, ½ tsp salt, ½ tsp cinnamon
Add the dry ingredients to the butter mixture in two increments, alternating with the buttermilk. Mix on low speed until just combined.
½ cup buttermilk
In a small bowl, toss the blueberries with a tablespoon of all purpose flour until well coated. Add the berries to the batter and fold them in gently with a spatula.
⅔ cup fresh blueberries, 1 tbsp all purpose flour
Spoon the batter into each muffin cup, filling them until ¾'s full. Place them in the center rack of the oven and bake for 18-20 minutes until springy to the touch and golden on the edges. A toothpick should come out clean when inserted.
Remove muffins from the oven and let them cool completely before removing them from the pan. Enjoy!