Preheat oven to 375°F (190°C). Grease one 8x8 inch pan.
Cream together 3/4 cup sugar, shortening, and egg. In a separate bowl mix together 2 cups flour, baking powder, and salt. Stir into sugar mixture, alternating with milk. Stir in plums and pluots. Pour into greased 8x8 inch pan.
To make topping: Combine the sugar, flour, cinnamon, and butter. Sprinkle over cake batter. Bake for 25-30 minutes.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.