Preheat the oven to 400 degrees and line 24 muffin cups with liners.
Prepare the peaches by bringing a small pot of water to a boil. Boil the peaches for 45 seconds. Then remove them from the boiling water and submerge them in ice water. After 1 or 2 minutes take them out of the ice water and the skins should peel right off with a little gentle rubbing. Slice and dice peaches to get 2 cups of peaches.
In a mixing bowl, cream the butter and sugar. Beat in the eggs and vanilla. Beat in the baking powder, baking soda, and salt.
Whisk together the sour cream and milk in a measuring cup to add alternately with the flour.
Stir in ⅓ of the flour, then ½ the sour cream/milk, another ⅓ of the flour and last ½ of the sour cream/milk. Fold in the peaches with the last of the flour. Divide the batter up among 24 muffin cups.
In a food processor or in a bowl with a fork, stir the brown sugar, flour and ground cinnamon together. Cut in the butter until well combined and crumbly. Sprinkle over the tops of the muffins.
Bake at 400 degrees for 15-18 minutes. A toothpick should come out clean.