In a bowl, mix the flour, baking powder, baking soda, salt, and cinnamon.
In another bowl, combine the eggs, granulated sugar, milk, sour cream, and apples.
Gradually add the flour mixture to the egg mixture, stirring as you go.

Spray a muffin tin with nonstick cooking spray and divide the batter evenly among the cups.
Mix the brown sugar with the teaspoon of cinnamon and sprinkle over the muffins.
Preheat the oven to 400°F (204°C).

Bake the muffins for 35 minutes, or until a toothpick inserted in the center comes out clean.
Let cool, then remove the muffins from the tin while still warm and place on a wire rack to cool completely.