Preheat the Oven: Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners or grease it lightly.
Prepare the Peaches: If using fresh peaches, peel, pit, and chop them into small cubes. If using canned peaches, drain and chop them. Toss the diced peaches in a tablespoon of cornstarch to prevent them from releasing too much juice during baking. Set aside.
Mix Dry Ingredients: In a large bowl, combine the flour, granulated sugar, baking powder, salt, and cinnamon (if using). Stir until well mixed.
Mix Wet Ingredients: In a separate bowl, whisk together the milk, melted butter, egg, and vanilla extract until smooth.
Combine: Pour the wet ingredients into the dry ingredients and stir until just combined. The batter will be a little lumpy, which is fine. Be careful not to overmix.
Fold in Peaches: Gently fold in the diced peaches, ensuring they are evenly distributed throughout the batter.
Fill Muffin Tin: Spoon the batter into the prepared muffin tin, filling each cup about 3/4 of the way full.
Make the Topping: In a small bowl, mix the brown sugar and cinnamon together. Sprinkle this mixture evenly over the tops of the muffin batter in each muffin cup.
Bake: Bake for 18–22 minutes or until a toothpick inserted into the center comes out clean or with a few crumbs. The muffins should be golden brown on top.
Cool: Let the muffins cool in the tin for 5 minutes, then transfer them to a wire rack to cool completely.
