Confectioners' sugar (optional), for decorating cake
2 baking apples, peeled, cored and cut into 1/2-inch cubes (I like Honeycrisp, Fuji or Granny Smith) (3-1/2 - 4 cups chopped)
3 tbsp. dark rum
1 tsp. vanilla extract
2 large eggs
2/3 cup granulated sugar, plus more for sprinkling over cake
1 stick (1/2 cup) unsalted butter, at room temperature
1/4 tsp. salt
1 tsp. powder
1 cup all-purpose flour, spooned into measuring cup and leveled-off