Preheat oven to 375.
Grease 9 x 10 or 10 x 10 baking dish.
Mix vinegar and milk then set to side.
Mix together 2 cups flour, sugar, baking powder, and salt.
Melt 1/4 cup butter.
Whisk together milk, egg, and butter.
Mix wet and dry ingredients together.
Put half of batter into baking dish.
Layer peach slices over top of batter.
Dice remaining 3 tablespoons of butter into small cubes.
Add butter and remaining 1/4 cup flour into remaining 1/2 of batter.
Gently mix together until incorporated and spread over top of peaches.
Bake approximately 1 hour, until toothpick comes out clean when testing the middle of the cake.