Preheat the oven to 400°F. Spray or line a muffin tin. Set aside.

To make the streusel mix together ¼ cup of brown sugar, ½ teaspoon of cinnamon, and 2 tablespoons of flour in a small bowl. Mix in 1 tablespoon of butter or margarine, I like to use a fork to mix the butter in until the mixture resembles a crumble. Set aside. 

To make the muffin batter whisk together 2 cups of all-purpose flour, 1 tablespoon of baking powder, ½ teaspoon each of salt, and ground cinnamon in a medium bowl. Set aside.

Beat ½ cup of unsalted butter on high speed until smooth and creamy, about 1 minute. Add ⅓ cup of brown sugar, and ¼ cup of white sugar and continue beating for additional 2 minutes. Add in 2 eggs, and 2 teaspoons of vanilla extract and beat until combined. Reduce mixture to low and alternate adding the flour mixture with ¾ cup of milk beginning and ending with flour. Fold in 1 and ¼ cups of peeled and diced peaches (about 3 peaches).

Spoon into the prepared muffin tin to the tops. Press the streusel mixture into the top of each muffin.

Bake in preheated oven for about 20 minutes or until a toothpick inserted in the center comes out clean or with a few moist crumbs. Let cool on a wire rack for about 10 minutes in the pan before removing to wire rack to cool completely.

To make the glaze, whisk together 1 cup of sifted icing sugar with 1 tablespoon of milk or heavy cream and ½ teaspoon of vanilla. Drizzle over warm muffins.