Grease the inside of 12 muffin cups with melted butter or line a muffin tin with holders. If using butter, place the tin in the freezer to solidify the butter while you prepare the rest of the ingredients.
Melt the butter in a heavy-bottomed pan over medium heat, stirring as the butter forms and turns golden brown with brown specks in the bottom of the pan. When the butter browns, remove from heat and let cool for a few minutes. Whisk in the vanilla and almond extract.
Meanwhile, combine the flour, almond meal, powdered sugar, and baking soda in the bowl of a stand mixer with the paddle attachment on low speed.
Add the egg whites and mix again on low speed until combined.
Add the browned butter and mix again on low until just combined and smooth.
Divide the batter among the 12 prepared muffin cups.
Add 2 slices of peach on top.
Bake for about 12 to 15 minutes, or until a toothpick stuck in the middle has only a few crumbs. Transfer to a wire rack to cool. Serve slightly warm.
