Prepare topping: In small bowl stir together the flour, sugar and cinnamon; with a fork, work in the butter until crumbly. Refrigerate until needed. Preheat oven to 200ºC . Line dozen muffin cups with paper liners or generously butter the cups and the top of the pan around the muffin cups. In a medium bowl, whisk the egg. Then whisk in the sour cream, milk, vanilla and melted butter. Stir in the diced peaches. In a large bowl, stir together the flour, sugar, baking powder, baking soda and salt. Pour in the sour cream-peach mixture all at once and stir quickly, just to moisten; the batter will be thick and lumpy. Spoon into muffin cups, dividing it equally until the cups are full. Quickly crumble the topping over the batter. Bake at 25 to 30 minutes or until golden brown. The tops will spring back when lightly touched. Let cool in the pan for 5 minutes and then carefully remove and cool on a rack. Cool 10 to 15 minutes. Serve warm.