Preheat your oven to 350°F (175°C). Line a standard muffin pan with paper liners.

In a large mixing bowl, whisk together all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Set aside.

In a separate bowl, mix milk, melted unsalted butter, eggs, and vanilla extract until smooth.

Gently pour the wet mixture into the dry ingredients. Fold together until just combined.

Fold in diced peaches gently.

Spoon the muffin batter into the prepared muffin cups, filling each about two-thirds full.

In a small bowl, combine brown sugar and ground cinnamon. Mix until blended.

Sprinkle the topping mixture over each muffin cup.

Bake for 18–20 minutes until golden brown and a toothpick comes out clean.

Cool the muffins for about 5 minutes before transferring to a wire rack.