Preheat your oven to 425°F and line a muffin pan with paper liners. While the oven heats, make the crumb topping by combining the 1/2 cup flour, granulated sugar, brown sugar, and nutmeg in a bowl. Add the cold cubed butter and use your fingertips to work it into the flour mixture until it resembles coarse breadcrumbs with pea-sized pieces of butter throughout. Transfer the crumble mixture to the refrigerator—the cold butter helps create a crispy, textured topping.

In a separate bowl, whisk together the 2 cups flour, baking powder, cinnamon, and salt. Set this dry mixture aside. Peel and dice your peaches into bite-sized pieces—I find it helpful to dice them right before mixing into the batter so they stay fresh and don't release too much liquid that could make the muffins soggy.

In a large bowl, beat together the melted and cooled butter with the sugar for about 2 minutes until well combined and slightly lighter in color. Add the room-temperature eggs one at a time, beating for about 1 minute total to fully incorporate them with the vanilla extract. Working with room-temperature eggs helps them incorporate smoothly into the butter mixture, creating a more uniform batter.

Gently fold the dry ingredient mixture from Step 2 into the wet batter from Step 3, alternating with the milk—add about a third of the dry mixture, then half the milk, then another third of the dry mixture, then the remaining milk, and finish with the last of the dry mixture. This technique prevents overworking the batter. Fold in the diced peaches just until evenly distributed. Divide the batter evenly among the muffin cups, filling each about two-thirds full. Top each muffin with a few diced peaches and a generous spoonful of the chilled crumb topping from Step 1.

Place the muffin pan in the preheated 425°F oven and bake for 5 minutes. This initial high heat jump-starts the rise and helps set the structure. Then reduce the oven temperature to 350°F and continue baking for 15–18 minutes until the muffins are golden brown and a toothpick inserted into the center comes out clean or with just a few moist crumbs. The temperature drop prevents the tops from browning too quickly while the interiors finish cooking.

Remove the muffin pan from the oven and let the muffins cool in the pan for 5 minutes so they set slightly and won't fall apart when removed. Transfer them to a wire cooling rack for at least 10 minutes before serving. This cooling time allows the crumb topping to firm up and the muffins to finish setting internally, giving you the best texture.