3large peachespeeled and chopped + 1 large peach, sliced, for topping
Preheat oven to 375ºF. Line a 12-cup muffin pan with paper liners, or grease with butter.
Add all streusel ingredients to a small bowl and work them together with fingers until coarse crumbs form; set aside.
In a large bowl, whisk together flour, sugar, baking soda, baking powder and salt. In a separate bowl, whisk together the sour cream, oil, eggs and vanilla extract. Add the sour cream mixture to the dry ingredients and gently fold together. When about 80% combined (there should still be floury patches), gently fold in the chopped peaches.
Spoon the muffin batter into prepared muffin pan and sprinkle streusel over tops. Add a peach slice to each. Bake 20-22 minutes, or until top feels springy when lightly pressed. Cool on wire rack.