Step 1

Preheat the oven to 325°F. Generously butter an 8 to 9-inch round dish (either a deep cake pan or a glass pyrex round dish). Rinse your plums before cutting each in half, removing the pits. Place the plums, flat side down, in your pie dish. Try to fit them in as neatly as you can without shoving in too many plums. Set aside.

Step 2

To a small saucepan, add 1/3 cup of water and 1 cup of the granulated sugar. Turn the heat onto medium high, allowing the mixture to come to a simmer. Do NOT stir the sugar mixture. Instead, swirl the mixture in the pan every so often. Do not take your eyes off the mixture; remove as soon as it turns a golden amber color.

Step 3

Evenly pour the amber sugar mixture over all of the plums. Let the liquid on the plums set. In the meanwhile, get started on your cake batter.

Step 4

Cream the unsalted butter and remaining 3/4 cup of sugar until fluffy. Add in the sour cream, lemon zest, and vanilla extract; mix just until combined. Add in the eggs, one at a time, stopping the mixture as soon as the eggs are incorporated.

Step 5

In a separate bowl, sift the flour, baking powder, and salt together. With the mixer running on medium low speed, add the flour mixture to the wet mixture. Stop the mixer as soon as it's all blended in; you don't want to over mix the batter. Use a rubber spatula to scrape up any batter from the bottom and sides of the bowl and give the entire batter a good stir.

Step 6

Pour the cake batter onto the sugar-set plums, evenly spreading out the batter. Bake the cake at 325°F for about 35 to 40 minutes on the lower middle rack. Once it looks like the entire cake has pretty much set except for a small part in the center, increase the heat to 350°F to bake for another 5 minutes. You'll see the center begin to set and the top of the cake become golden. Test the cake with a toothpick inserted in the center, it should come out clean or with just a tiny crumb or two.

Step 7

Let the cake rest in its pan for 5 minutes. Place a very large piece of parchment paper or wax paper over a flat serving plate before flipping the cake out onto the paper. The juices of the plums will probably run down the sides of the cake, which is why it's good to use the sheet of paper underneath. After about 1/2 an hour or so when the cake's juices aren't so runny, you can slide the cake off the sheet and onto the plate, or just leave as is. This is also the point in which you can dust some powdered sugar on top of the cake if you like.