In a large bowl, cream the butter and 1 cup of sugar for about 3 minutes until light and fluffy.
1/2 cup (114g) unsalted butter, 1 cup granulated sugar
Then beat in the egg and vanilla until combined.
1 large egg, 1 tsp vanilla extract
Add 1/3 of the flour mixture at a time to the wet ingredients, alternating with 1/2 the milk, mixing at low speed until just combined and smooth.
1/2 cup milk
Transfer the batter into the prepared pan. Arrange the plums on top and sprinkle with the remaining 2 tablespoons of sugar on top.
8-10 plums, 2 Tbsp granulated sugar
Bake at 350F for 45-60 minutes or until golden on top and a toothpick inserted into the center comes out clean. Remove the springform edge and let cool on a wire rack. Serve with whipped cream or ice cream if desired.
Notes
Leftover cake can be covered and stored at room temperature for up to 3 days or in the fridge for up to 5 days.To Freeze - Once the cake is completely cooled, double wrap in aluminum foil or saran wrap and store in the freezer for up to 3 months. Thaw overnight on the counter before serving.