Preheat the oven to 375 degrees. Blanch the peaches in boiling water and slip off the skins. Coarsely chop the peaches, discarding the skin and pits.
Whisk together the brown sugar, flour, cinnamon and rosemary, and toss with the peaches. Pour into an 13 x 9 inch glass baking dish that you've sprayed with cooking spray.
Combine the sugar, flour, cinnamon, and baking powder in a medium bowl. Whisk to blend well. Add the egg and use your hands to mix thoroughly, and then sprinkle evenly over the peaches.
Spoon the butter evenly over the topping, and bake until the top is browned and the peaches are soft, about 30-40 minutes.
Serve crumble warm or at room temperature, garnished with crème fraîche.
Recipe by Cooking With Michele® at https://cookingwithmichele.com/2017/08/rosemary-peach-crumble/