Pineapple Pecan Upside-Down Cake

1/2 cup butter
1 cup brown sugar
1 (15 1/2 ounce) can pineapple slices, undrained
1/4 cup pecan halves
3 eggs, separated
1 cup granulated sugar
1 cup sifted cake flour
1 teaspoon baking powder
1/8 teaspoon salt

Melt butter in a 10-inch cast iron skillet. Sprinkle evenly with brown sugar. Drain pineapple, reserving 1/3 cup juice (set juice aside). Arrange pineapple slices over brown sugar, placing a half pecan in center of each pineapple slice.

Beat egg yolk until thick; add sugar, flour, baking powder, and salt. Stir in reserved pineapple juice. Beat egg whites to stiff peaks; fold in flour mixture. Spoon batter over pineapples. Bake at 375 degrees F for 30 minutes.