Preheat the oven to 375 degrees.

Grease a 9 inch cake pan or baking pan lined with parchment paper.

Using an electric mixer beat butter and sugars until light andf fluffy.

In a large bowl mix the flour,baking soda and salt.

With mixer on low,beat in eggs one at a time until incorporated.

Beat in vanilla.

Add in 1/2 of the flour mixture,then sour cream followed by the rest of the flour mixture.Mix until just combined.

Spread batter into pan and smooth the top with a knife.

Arrange the plums at the top.

Bake for 35-40 minutes or until the a toothpick inserted in the center comes out clean.

Dust with confectioner's sugar once cooled.