In a medium, mixing bowl, whisk together both flours (1 cup cake flour + 1 cup all-purpose flour), baking powder (1 teaspoon), baking soda (1 teaspoon), and salt (1/4 teaspoon); set aside.
In a large mixing bowl, using a hand-held electric mixer, cream together butter (1/2 cup) and sugar (1 cup) on medium speed until light and fluffy, about 3 minutes.
Add eggs (2) one at a time, beating just until the yolk disappears.
Add the flour mixture and buttermilk (1 cup) alternately, beginning and ending with the flour mixture, with the mixer on low, beating just until combined. Stir in the vanilla (2 teaspoons).
Gently spoon the batter evenly over the pineapple slices. Bake in preheated oven until golden brown and a toothpick inserted into the center of the cake comes out clean, 35 to 40 minutes.
Cool the cake in the skillet on a wire rack for 4 minutes only.
Remove the cake from the oven and cool on a wire rack for 4 minutes. Run a butter knife around the edge of the skillet and, wearing oven mitts and working quickly, invert the cake onto a cake plate, keeping the plate and skillet firmly pressed together.
Carefully lift the skillet off the cake and replace any fruit stuck to the bottom of the skillet, if necessary. Serve warm or at room temperature.