- Preheat your oven to 375℉ and prepare the muffin baking pan by adding paper muffin liners. I also recommend spraying the liners with cooking oil spray to help remove the muffins after baking. 
- Grab a large mixing bowl, and add flour, granulated sugar, brown sugar, baking powder, baking soda, and salt. Use a whisk (or mixing spoon if whisk is unavailable) to thoroughly mix all of these ingredients together. Set this bowl of dry ingredients aside. 
- In a separate mixing bowl, add in the 1 stick of melted butter, buttermilk, yogurt, egg and vanilla extract and mix until well combined. You can use a handheld mixer or stand mixer to mix. 
- Combine the wet ingredients and dry ingredients by slowly pouring the bowl of dry ingredients from Step #2 into the bowl of wet ingredients. Mix until just combined, do not overmix. 
- Now it’s time for the star of the show! Gently pour and fold in the diced peaches. 
- Grab your prepared muffin baking pan and divide the batter evenly between the muffin cups. I recommend filling each muffin cup anywhere between ⅔-¾ of the way full. You can sprinkle the tops with a bit of brown sugar, if desired. 
- Bake at 375℉ for 18-22 minutes or until a toothpick inserted into the center of one of the muffins comes out clean. 
- Carefully remove the muffins from the oven and allow to cool for 5-10 minutes.