I heart my neighbor's plum tree!

Sweet and Tart!
Yesterday afternoon my neighbor, Richard, came by with a huge bowl of super sweet italian plums. His tree is going off, and he has more plums than he and his family can handle. In between gorging myself on plums today, I decided to make a Caramelized Plum Up-side Down Cake. This spongy, fruity cake is great for both dessert and breakfast.
I made one cake with peaches and the other with plums. The one with plums only was a bit too tart for my tastes, but I think that I'd really like a mix of stone fruits better than any one fruit by itself.
I hope my friends enjoyed!

Caramelized Stone Fruit Up-Side Down Cake
enough plums, peaches, pluots, cherries, etc... to cover the bottom of your baking dish when cut and fleshy parts are face-down.
1 1/2 c sugar
1/4 c butter (room temperature)
1 Tbs olive oil
1 tsp vanilla extract
1 egg (room temperature)
2/3 c milk (room temperature)
1 1/3 c flour 2 tsp baking powder
1/4 tsp kosher salt

1. Preheat oven to 350 F (put on convection if you can). Liberally butter a pie dish.
2. Coat fruit with about 1/2 cup sugar (more or less depending on sweetness of the fruit). Heat oil in a hot skillet, add plums and cook 2-3 minutes to caramelize. Carefully remove fruit and add to pie dish, flesh side down. Try to make it pretty as this will become the top of the cake.
3. Cream 1 cup sugar, and 1/4 cup butter. In a separate bowl mix together vanilla, egg, and milk. In a separate bowl sift together flour, baking powder and salt. With the mixer on low speed alternately add the dry and wet ingredients, just until combined (start and end with dry ingredients). Finish mixing with a rubber spatula.
4. Pour batter over the fruit, pop into the oven, and let bake for 50 minutes (or until a toothpick inserted into the middle comes out clean). Let cool 20 minutes and invert onto a platter. Note that if you wait too long to invert, the cake is more likely to stick to the pie dish.
5. Eat! *Tastes best warm or at room temperature, but is not bad cold.