Preheat the oven to 375°F (190°C). Grease a muffin tin or line it with paper liners.

In a bowl, mix together 3/4 cup of all-purpose flour, 2/3 cup sugar, softened butter, and cinnamon until combined.

In another bowl, whisk together 2 cups of all-purpose flour, baking powder, and salt.

In a separate bowl, beat the eggs and then add in 1 cup of sugar, vanilla, vegetable oil, and sour cream until smooth.

Gradually combine the dry ingredients with the wet ingredients.

Gently fold in the blueberries and the remaining flour (1 tablespoon) to prevent sticking.

Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.

Bake in the preheated oven for about 20-25 minutes, or until a toothpick comes out clean.

Let cool in the tin for a few minutes before transferring to a wire rack.