Preheat oven to 425°F (218°C). Spray a 12-count muffin pan with nonstick spray or line with cupcake liners. Set aside.

Mix the brown sugar, granulated sugar, cinnamon, and melted butter together in a small bowl until combined. Add the flour and use a fork to gently mix until crumbs form. Don’t over-mix into a paste. Just mix until it is crumbly. Set aside.

Whisk the flour, baking soda, baking powder, cinnamon, allspice, and salt together in a medium bowl. Set aside.

In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter and both sugars together on high speed until smooth and creamy, about 3 minutes. Scrape down the sides and bottom of the bowl as needed. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Add the eggs, yogurt or sour cream, and vanilla extract. Beat on medium speed for 1 minute, then turn up to high speed until the mixture is combined and mostly creamy. (It’s ok if it appears somewhat curdled.) Scrape down the sides and bottom of the bowl as needed. With the mixer running on low speed, add the dry ingredients and milk into the wet ingredients and beat until no flour pockets remain. Fold in the chopped peaches.

Spoon the batter evenly into each cup or liner, filling each all the way to the top. Spoon crumb topping on each, gently pressing it down so it sticks.

Bake for 5 minutes at 425°F; then, without opening the oven, reduce the oven temperature to 350°F (177°C). Bake for an additional 16–19 minutes or until a toothpick inserted in the center comes out clean. The total time these muffins take in the oven is about 21–24 minutes. Allow the muffins to cool for 5 minutes in the muffin pan, then transfer to a wire rack to continue cooling. When warm, the muffins are quite fragile because of the wet peaches. Let them cool for at least 15 minutes before unwrapping and eating.

Whisk all of the icing ingredients together and drizzle over warm or cooled muffins.

Iced or plain muffins stay fresh covered at room temperature for a few days or in the refrigerator for up to 1 week.