This works best with purple Italian prune plums, as they are a dryer fruit and wont make the cake soggy. But if you can’t find them, other plums will work.
1 cup all-purpose flour
1 teaspoon baking powder
Large pinch of salt
1 cup granulated sugar plus 1 to 2 tablespoon (depending on sweetness of plums)
1/2 cup ( 8 tablespoons) unsalted butter, softened
2 large eggs
12 smallish purple Italian purple plums, halved and pitted
2 teaspoons fresh lemon juice
Heat oven to 350°F.
Sift or whisk together flour, baking powder and salt in a medium bowl. In a larger bowl, cream butter and 1 cup sugar together with an electric mixer until fluffy and light in color. Add the eggs, one at a time and scraping down the bowl, then the dry ingredients, mixing until just combined.
Spoon batter into an ungreased 9-inch springform pan and smooth the top. Arrange the plums, skin side up, all over the batter, covering it. Sprinkle the top with lemon juice, then remaining sugar.
Bake until cake is golden and a toothpick inserted into a center part of the cake comes out free of batter (but of course not plum juice), about 45 to 50 minutes. Cool on rack.
Once cool, DO NOT EAT! Wait until the next day, your wait will be worth it. The plumbs will release more juice and make the cake even better!