Blueberry Apricot Base:

1. Preheat the oven to 350 degrees.
2. In an oven safe skillet, like a cast iron skillet, melt butter and whisk in brown sugar until melted.
3. Add in blueberries and apricots and bring mixture to a simmer.
4. Sprinkle cornstarch over the mixture and simmer until the mixture thickens, about two minutes.
5. Turn heat off and remove from heat source.

For Cake:

1. In one mixing bowl, whisk together the flour, salt, and baking powder. Set aside.
2. In other mixing bowl, whisk together eggs, and white and brown sugar until the mixture is smooth and the sugar is dissolved.
3. Whisk in melted and cooled butter until smooth, then sour cream or greek yogurt, and lastly vanilla extract.
4. Fold the flour mixture into the wet mixture until just combined.
5. Spoon and gently smooth the cake over the top of the warm blueberry apricot mixture.
6. Bake in the oven for about 30 minutes. Check the cake after 25 minutes and monitor to ensure it is not cooking too fast.
7. Remove from the oven as soon as a toothpick inserted into the middle comes out clean. Let cool for 30 minutes, and serve warm.
8. Serve right out of the skillet with whipped cream and fresh berries on top, or gently flip out onto a serving platter like a true upside down cake.