Preheat oven to 425 F. Line a 12-cup muffin pan with paper cupcake liners or spray with nonstick cooking spray; set aside.

In a small bowl, combine the streusel topping ingredients with a fork or pastry cutter until it is crumbly; set aside.

In a medium mixing bowl, whisk together the flour, baking soda, baking powder, cinnamon, and salt; set aside.

In a large mixing bowl, use an electric mixer to beat together the butter, brown sugar, and granulated sugar until light and fluffy, about 2 minutes.

Add the eggs and mix until well incorporated.

Mix in the sour cream, milk, and vanilla, then add the dry ingredients and mix just until combined.

Fold in the chopped peaches.

Scoop the batter into the prepared muffin cups, evenly distributing all of the batter between the 12 cups. Top with the streusel topping and press the topping down lightly to be sure it sticks to the muffin batter.

Bake the muffins at 425 F for 5 minutes, then reduce the heat to 350 F and bake for another 16-18 minutes until a toothpick inserted into the center of the muffins comes out clean.

Cool the muffins in the pan for 5 minutes, then transfer to a wire cooling rack to cool completely.