Preheat your oven to 350°F (175°C). Grease and flour a standard 9x5 inch loaf pan, or line it with parchment paper leaving an overhang for easy removal.

In a large bowl, whisk together the flour, granulated sugar, baking powder, salt, and cinnamon until well combined.

In a separate medium bowl, whisk together the melted butter, beaten eggs, milk, and vanilla extract. Pour the wet ingredients into the dry ingredients and mix gently until just combined. Do not overmix; a few lumps are acceptable.

Gently fold in the diced fresh peaches. Pour the batter evenly into the prepared loaf pan.

If using the optional topping: In a small bowl, combine the brown sugar, flour, and nutmeg. Cut in the cold butter using your fingers or a pastry blender until the mixture resembles coarse crumbs. Sprinkle evenly over the top of the batter.

Bake for 50 to 60 minutes, or until a wooden skewer inserted into the center comes out clean or with moist crumbs attached. If the top browns too quickly, loosely tent the loaf with foil.

Let the bread cool in the pan for 10 minutes before carefully removing it to a wire rack to cool completely before slicing and serving.