Preheat oven to 350°F and prepare a muffin tin with cupcake liners.
Sift together the flour, baking powder, baking soda and salt. Set aside.
In a separate large mixing bowl or mixing bowl of a stand mixer fitted with the paddle attachment, beat the butter for 1-2 minutes until creamy and pale.
Add the sugars and continue to beat until fully combined. Beat in the eggs, one at a time. Lastly, add the vanilla extract, blend until smooth.
Alternate adding the buttermilk, flour mixture and seltzer water until all ingredients are just combined.
Fill each wrapper 1/3 way. Spoon 1 heaping tablespoon of the peaches on top of batter followed by an additional dollop of cake batter to cover.
Bake for 18-20 minutes, or until the tops gently bounce back when touched and are slightly browned. Cool completely.