HEAT oven to 375°F. BEAT butter and sugar in mixer bowl on medium speed until light and fluffy. ADD eggs and vanilla; BEAT until well-blended.

MIX flour, baking powder and cinnamon in medium bowl. ADD to egg mixture; BEAT on low speed until smooth. FOLD in 3/4 cup of the plums. SPREAD batter in greased 9-inch round baking pan. TOP evenly with remaining plums.

BAKE in 375°F oven until top is lightly browned and center springs back when lightly tapped with finger, 30 to 35 minutes. COOL on wire rack.