One 9-inch round cake pan
1 pound small navel oranges, blood oranges, Cara Cara oranges, or a combination (2 to 3 oranges)
10 Tbsp unsalted butter, melted, divided
1-1/2 cups granulated sugar, divided
1 tsp cornstarch
1/8 tsp plus 1/2 tsp salt, divided
1 cup AP flour
1 tsp baking powder
1/2 cup...