Preheat oven to 425°F (218°C). Spray a 12-count muffin pan with nonstick spray or line with cupcake liners. Set aside.
In a large bowl, whisk together the dry ingredients: the flour, baking powder, baking soda, cinnamon, and salt together. Set aside.
In another bowl, beat butter and brown sugar for about 2 minutes. Now whisk in the eggs together until the yolks and whites are blended. Then add sour cream and vanilla.
Add the liquid mixture from to the dry ingredients mixture in step 2. Mix well with a wooden spoon.
Add the milk and continue to beat on low until combined.
Use a large spoon or an ice cream scoop to fill each muffin cup completely full.
Bake the muffins for 5 minutes at 425 then, keeping the muffins in the oven, reduce the oven temperature to 350°F. Bake for an additional 15-18 minutes or until a toothpick inserted in the center comes out clean.
Allow the muffins to cool for 5 minutes in the muffin pan, then transfer to a wire rack to continue cooling.