Instructions: Put rack in center of oven & heat to 350. Butter 9" springform pan.

Mix 1/2 cup butter with 1/2 cup sugar, 1/2 tsp. cinnamon, egg, sour cream & vanilla with mixer or metal blade of food processor until smooth & light. Add flour, baking powder, baking soda & salt & mix just until combined. Transfer batter to pan. Smooth out with spatula. Arrange apple slices, overlapping, in a circle around outer edge, filling in center with slices tucked attractively into place to cover batter. Dot with remaining butter. Combine remaining 1/4 cup sugar & 1/2 tsp. cinnamon. Sprinkle over apples. Bake until well browned & wooden pick inserted into center comes out clean, about 1 hour. Cool in pan for 10 minutes. Use knife to loosen cake from sides of pan & remove sides of pan. Serve warm. Can be made a day ahead & refrigerated once it is completely cooled, uncovered. Reheat, uncovered, in 350 oven until barely warm, not hot, about 10 minutes.

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