Preheat the oven to 350 degrees F. Place a sheet of parchment paper over the bottom disk of an 8-9 inch springform pan. Fasten the ring around the disk with the parchment paper secured in between. Cut off the excess paper. Grease the sides of the pan.
Whisk together the flour, baking powder, salt and 1/2 teaspoon of pumpkin pie spice.
In the electric mixer, cream 1 cup of sugar with the butter. Add the eggs one at a time. Slowly add the flour mixture. Scrape the bowl and mix again.
Spread the batter evenly in the prepared pan. Slice the plums into eighths. The easiest way I’ve found to do this, is to run a knife around the plum to halve it, then do the same to quarter it. Split each quarter in half. The little sections should pop off the pit with your knife.
Place the plum slices around the top of the cake in a pretty pattern. Make sure they are close together. Sprinkle 1 tablespoon of sugar and the remaining 1/4 teaspoon pumpkin pie spice over the plums. Bake for 45-55 minutes, until a toothpick inserted into the center comes out clean. Make SURE not to overbake! Cool for 15 minutes in the pan, and another 10 minutes out of the pan before serving!
Also try with fresh summer peaches, nectarines, or apricots!