Juicy peaches give this Peach Crumb Cake a soft, fruit-filled center that pairs perfectly with the warm spice of cinnamon and a brown sugar topping that crisps up with every bake.
Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Lightly spray an 8×8″ baking dish or a 9″ round baking dish, set aside.
In the bowl of a stand mixer, beat together the butter, sugar, and vanilla until light and fluffy (about 2 minutes). Add the egg, then the egg yolk, mixing until combined.
In a small mixing bowl, whisk together the flours, baking powder, salt, and cinnamon.
With the mixing speed on low, alternate adding the flour mixture with the sour cream and buttermilk into the mixture of butter, sugar, vanilla, and eggs. Mix until well combined and no flour pockets remain. The cake batter will be relatively thick.
Remove the bowl from the stand and spread the batter evenly into the prepared pan.
Layer the sliced peaches on top, making sure to completely cover the batter.
In a small mixing bowl, combine all crumb topping ingredients. Using a pastry blender, cut the butter into fine pieces, creating tiny lumps in the mixture. Pour the mixture over the peaches and spread evenly.
Place in oven and bake for 35–40 minutes or until a toothpick inserted into the center of the cake comes out clean (baking in a round dish typically takes about 38 minutes). The topping should be browned, and the center should look slightly moist. Remove from oven and allow to cool for 30–45 minutes before serving.
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Notes
To STORE leftover Peach Crumble Cake, allow it to cool completely. Cover the dish with foil or transfer individual pieces to an airtight container and keep at room temperature for up to 2 days. For longer storage, place the cake in the refrigerator for up to 4–5 days.To FREEZE, wrap tightly in plastic wrap and place in a freezer-safe container or bag—freeze for up to 2 months. Thaw in the fridge overnight or on the counter for a couple of hours. REHEAT slices in the microwave for 10–15 seconds or in a warm oven until just heated through.