- Preheat the oven to 350 F.
- Grease and flour a 9-inch springform pan or spray with baking spray with flour.
- Slice peeled pluots or plums thinly and toss them in a bowl with 1/4 cup of the granulated sugar; set aside.
- In a large mixing bowl with an electric mixer, beat the 3/4 cup of butter and 1 cup of the granulated sugar until light and fluffy. Beat in eggs, one at a time, beating well after each addition. Beat in the vanilla.
- In a separate bowl, combine the 1 3/4 cups of flour, baking powder, and salt. Slowly blend the dry ingredients into the first mixture until the batter is smooth. The batter will be thick.
- Spread the batter in the prepared baking pan. Arrange the sliced pluots or plums all around in a concentric circle, overlapping slightly. Fill in gaps and overlap with any leftover slices of fruit. Sprinkle the sugar and cinnamon mixture evenly over the fruit.
- If desired, top with the streusel topping, if using (see below).
- Bake the cake for about 1 hour and 10 minutes to 1 hour and 20 minutes, or until a toothpick or cake tester inserted near the center of the cake comes out clean.
- In a bowl, combine the 1/2 cup of brown sugar, 3/4 cup of flour, 1/2 teaspoon of cinnamon, 1/4 teaspoon of nutmeg, and 5 tablespoons of melted butter. Mix with fingers or a fork until crumbly. Sprinkle over the fruit topping.
- Serve and enjoy!