brown sugar, firmly packed
peaches, peeled, cut in 1" chunks (2 cups)
Preheat oven to 350 degrees.
Grease 9" square baking pan.
Make streusel: Combine oats, flour, brown sugar and cinnamon in medium bowl.
With pasty blender or 2 knives, cut in butter until mixture resembles coarse crumbs.
Combine flour, baking powder, baking soda and salt in medium bowl.
Beat butter and sugar in mixer bowl at medium speed until light and fluffy.
Beat in eggs one at a time, then add vanilla.
Add sour cream alternately with dry ingredients, beginning and ending with dry ingredients; beat just until combined.
Spread batter in prepared pan.
Sprinkle evenly with half the streusel.
Spoon peaches on top; sprinkle with remaining streusel.
Bake 50-60 minutes, until toothpick inserted in center comes out clean.
Cool in pan on wire rack 30 minutes.
Sprinkle with confectioners' sugar.
Serve warm or at room temperature.