7 tablespoons sugar, divided, plus 3/4 cup sugar
3 tablespoons water
8 tablespoons (1 stick) unsalted butter, room temperature, divided
3 unpeeled small to medium blood oranges
3/4 cup plus 3 tablespoons unbleached all purpose flour
3 tablespoons polenta or coarse yellow cornmeal (preferably stone-ground)
1 1/2 teaspoons baking powder
1/4 teaspoon coarse kosher salt
3/4 teaspoon vanilla extract
2 large eggs, separated
6 tablespoons whole milk

Whipped crème fraîche to serve:
1 cup chilled crème fraîche
2 tablespoons sugar