Step 1

Preheat oven to 350°F. and butter and flour a 9-inch round or square baking pan at least 2 inches deep.

Step 3

Make streusel

Step 5

In a food processor pulse together streusel ingredients until combined well and crumbly.

Step 6

Make cake batter:

Step 7

In a bowl with an electric mixer beat butter with sugar until light and fluffy

Step 8

Add eggs, 1 at a time, beating well after each addition, and vanilla

Step 9

Sift in flour with baking powder and salt and beat until just combined

Step 10

Spread cake batter in pan, smoothing top, and arrange plum slices over it in slightly overlapping concentric circles.

Step 11

Sprinkle streusel over plum slices

Step 12

Bake cake in middle of oven 1 hour, or until a tester comes out clean Cool cake slightly on a rack and sift confectioners' sugar over it

Step 13

Serve coffeecake warm or at room temperature.