Glutenfree Butterless Pineapple Cherry Upside-down Cake

I dont usually go around looking for butterless cakes. But when I had a sudden craving for upside-down cakes, thanks to C, and I was all out of butter - I absolutely had no choice but to come up with this version. Apparently, all I had to do was substitute 1/2 cup of pineapple puree for 1 cup of butter, and reduce the sugar. Look at that cake, can't believe it is gluten-free even after tasting it :)

Recipe:

Adapted from SmittenKitchen's Cherry Cornmeal Upside-Down Cake

1/2 cup crushed fresh pineapple, divided

1/4 cup (packed) dark brown sugar2 teaspoons balsamic vinegar1 cup whole pitted fresh  sweet cherries 
1/4 cup yellow cornmeal (preferably stone-ground medium grind)
2 teaspoons baking powder
1/4 teaspoon salt
1/2 cup sugar
2 large eggs, separated
3/4 teaspoon pineapple extract
1/2 cup whole milk
1/2 pineapple cored and sliced into semicircles
1 cup fine milled rice flour
1/4 cup tapioca flour
1 teaspoons xanthan gum

Position rack in center of oven; preheat to 350°F. 

Combine 1/4 cup crushed pineapple with brown sugar and vinegar in 10- to 11-inch ovenproof skillet with 2-inch-high sides. Stir over medium heat until sugar dissolves. Increase heat to high; add cherries and sliced pineapples and bring to boil. Remove from heat.

Whisk flour, cornmeal, xantham gum,baking powder, and salt in medium bowl to blend. 

Stir crushed pineapple, pineapple extract and milk.

Using electric mixer, beat in egg yolks  and sugar; until pale. Add flour mixture alternately with milk mixture in 2 additions each, beating just until blended and occasionally scraping down sides of bowl. 

Using clean dry beaters, beat egg whites in another medium bowl until stiff peaks. Using rubber spatula, fold 1/4 of whites into batter to lighten slightly. Fold in remaining whites in 3 additions. 

Spoon batter over cherries and pineapple in skillet, then spread evenly with offset spatula to cover cherries.

Bake cake until top is golden brown and tester inserted into center comes out clean, about 45 minutes. 

Cool in skillet on rack 5 minutes. Run spatula around edges of cake to loosen. Invert onto serving platter. Leave skillet atop cake 5 minutes. Remove skillet. If necessary, rearrange any cherries that may have become dislodged. 

Let cake cool at least 45 minutes. Cut cake into wedges and serve slightly warm or at room temperature.