Melt 1/4 cup butter in a 10-inch cast-iron skillet over low heat; stir in rum. Sprinkle brown sugar evenly over butter mixture. Remove from heat.
Cut bananas in half crosswise; cut each half lengthwise into 3 slices. Arrange banana slices in a spoke pattern over syrup. Cut cherries in half and place 1 cherry half between each banana slice. Place remaining whole cherry in center of skillet.
Beat remaining 1/4 cup butter and 1/2 cup granulated sugar in a large bowl at medium speed with an electric mixer until blended. Add egg yolks, 1 at a time, beating just until blended after each addition. Add coconut milk, sour cream, and vanilla, beating just until blended. Combine baking mix and cinnamon. Add cinnamon mixture to milk mixture, beating just until blended.
Beat egg whites in a large bowl with an electric mixer until soft peaks form. Gradually beat in remaining 1/4 cup granulated sugar until stiff peaks form. Fold into batter. Spread batter evenly over bananas. Top with whip cream.
Bake at 350° for 45 to 50 minutes or until a wooden pick inserted in center comes out clean. Cool in skillet on wire rack 10 minutes. Invert cake onto a serving plate. Serve warm with whipped cream, if desired.