Preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius) and prepare a large muffin tin with 12 muffin cups.
Add the flour, baking powder, salt and sugar to a large bowl and whisk together to combine.
Add ¾ c of the peaches and stir well to coat.
Add the milk, egg, oil and vanilla extract, and stir together with a rubber spatula just until the flour disappears.
Portion the batter out into the muffin cups evenly (about ¾ full).
Combine the flour, sugar and cinnamon and baking powder in a small bowl and stir.
Add the cold butter in chunks and break it up with your fingers in the flour mixture until it resembles coarse crumbs.
Top the muffins with the remaining peaches and with a spoonful of the streusel topping.
Bake at 350 degrees Fahrenheit (175 degrees Celsius for about 20 minutes until golden brown and a toothpick inserted into one of the muffins comes out clean.
