To make the streusel topping, melt the butter and mix in the granulated sugar, brown sugar, and cinnamon. Slowly mix in the all-purpose flour using a fork. You want to use the fork to fluff the topping into a crumbly topping, not a paste. Set aside.

Preheat the oven to 425℉/220℃/Gas Mark 7. Line the muffin tin with muffin liners.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and cinnamon. Set aside.

In a large bowl, cream the softened unsalted butter with the granulated sugar and brown sugar. Beat on medium speed for about 3 minutes scraping down the sides of the bowl as needed.

Add the eggs, sour cream, and vanilla extract. Beat on medium speed for another 2 minutes until fully incorporated. Then add the dry ingredients, whole milk, and fully mix together.

Fold in the finely chopped peaches.

Take the muffin batter and fill each of the muffin liners to the top. Sprinkle the streusel topping generously on top of the muffin batter.

Bake for 5 minutes at 425℉/220℃/Gas Mark 7 then decrease the heat to 350℉/175℃/Gas Mark 4 and continue to bake for another 16-19 minutes.

Remove from the oven and insert a toothpick to ensure doneness. Let cool for 5 minutes in the muffin tin then remove muffins and place onto a cooling rack to continue to cool. Serve and enjoy!