Make topping: Bring 1/3 cup water to a boil in a saucepan. Add apricots and cherries; cover and set aside for 30 minutes. Drain, reserving soaking liquid.
Pour butter into a 9-inch round cake pan. Arrange apricots, cut side up, in pan; spoon cherries on top and sprinkle with brown sugar. Drizzle with soaking liquid.
Make cake: Preheat oven to 350°F. Mix flour, baking powder, cinnamon and salt.
Beat butter, sugar, egg and vanilla on medium speed until fluffy, scraping sides of bowl. Reduce speed; beat in milk gradually. Add flour mixture; beat until blended. Spoon batter into pan.
Bake until a cake tester inserted in center comes out clean, 35 to 40 minutes. Cool on a rack for 5 minutes. Loosen edges of cake. Place plate over pan; carefully invert cake. Remove pan. Serve warm.