Preheat the oven to 350F.

In the bowl of a stand mixer, beat together the butter and sugar until light and fluffy. Add in the eggs, one at a time, then beat in the vanilla.

Add in the flour, baking powder, and salt, and beat until combined.

Butter and flour a 9-inch springform cake pan, and pour in the batter.

Thinly slice your plums, and arrange them on top of the cake. Squeeze the lemon juice on top, then sprinkle a generous amount of cinnamon and sugar on top of the plums.

Bake for 45-50 minutes, until cake is fluffy and golden brown, and a toothpick inserted in the center comes out mostly clean {disregarding the plum juice}. Let cool slightly and enjoy!