Grease the bottom of an 8x8 glass pan or casserole dish.
Peel and pit the peaches, slice and place in a large bowl.
Mix in sugar, flour, cinnamon and vanilla. Toss to coat. Set aside while preparing topping.
Make the streusel by cutting the cold butter into a bowl, adding flour, sugar and cinnamon, and rubbing it with your fingers until the streusel is a coarse, sandy texture.
Put the peach mix into the pan, top generously with the streusel, and bake at 350° about 30 minutes, or until the streusel is golden brown and the peach juice is starting to bubble up through the topping. Enjoy!