These are cake-like muffins. For more traditional, crumbly muffins, follow method at the bottom of the page.
1 stick (1/2 cup) butter, softened
1 cup sugar
2 eggs
1 tsp vanilla
1/4 tsp cinnamon
1/2 tsp lemon zest
1/2 cup buttermilk (or 2 tbsp sour cream + milk to make 1/2 cup)
2 cups flour, separated
2 tsp. baking powder
1/2 tsp salt
2 cups fresh blueberries, rinsed and patted dry (still damp)
Cream the butter and sugar. Add egg and mix thoroughly. Mix in the cinnamon and lemon.
Place 1 cup of flour in a bowl, add the blueberries and toss to coat. Set aside.
Sift together the other cup of flour, baking powder, and salt.
Add dry ingredients to butter mixture, alternately with buttermilk.
Fold in the coated blueberries together with all the flour they're coated in.
Place paper muffin liners in muffin pan & spray with Pam. Spoon batter into muffin liners. Bake 375 30 minutes. Allow to cool in muffin liner about 10 minutes, then remove to cooling rack.
FOR TRADITIONAL, CRUMBLY MUFFINS:
Melt the butter & allow to cool a few minutes. Mix together the melted butter, buttermilk, and eggs; set aside.
Place 1 cup of flour in a bowl, add the blueberries and toss to coat. Set aside.
In a large bowl, whisk (by hand) together the other cup of flour, sugar, baking powder, salt, and cinnamon. Stir in the lemon zest. Make a well in the middle of the dry mixture and pour in the butter/milk/egg mixture. Mix with a spoon by hand just until moistened. (There will still be dry spots and lumps; that's okay.) Fold in the remaining flour and the coated blueberries, just until the blueberries are well distributed.
Follow above directions for preparing muffin liners and baking the muffins.