Skillet Baked Pineapple Upsidedown Cake

This may not look like anything exciting, but when you cut into it and taste the super moist, fresh-cut pineapple on the bottom... You'll realize it's pretty amazing. I got this recipe from Rick Bayless' cookbook Mexican Everyday.
Serves 8
3 oz (6 tbsp) butter, preferably unsalted
1/2 C firmly packed brown sugar
3 cups 1/2 inch-cubed, cleaned pineapple (you'll need about 3 quarters of a medium pineapple)
3/4 C all-purpose flour
3/4 C whole wheat flour (or additional all-purpose flour) (*I used whole wheat flour for the whole recipe and thought it came out great)
1/2 tsp salt
1/4 tsp baking soda
1 tsp baking powder
1 large egg
3/4 C white sugar
3/4 C buttermilk or plain yogurt

Turn on the oven to 375 degrees and position a rack in the middle. Melt the butter in a large 10 inch skillet, with an ovenproof handle, preferably non-stick, over medium heat. Swirl the butter in the skillet until it turns nut-brown, then pour it into a medium bowl. Without wiping the skillet, sprinkle the brown sugar evenly in the bottom. Top with the fruit in an even layer.
In a large bowl, whisk together the flours, salt, soda and baking powder. Add the sugar to the browned butter and whisk until thoroughly combined. Whisk in the egg, then the buttermilk or yogurt. Pour the wet ingredients into the bowl with the dry ones. Whisk thoroughly to combine.
Pour the batter evenly over the fruit in the skillet. Slide the skillet into the oven and bake about 35 minutes, until the cake is golden brown and springy to the touch at the center. Remove and let cool 10 minutes.
Invert a plate over the skillet, then holding plate and skillet firmly together with towels or pot holders, invert the two in one swift movement. Remove the skillet and the cake is ready to serve, it's best right out of the oven.
This makes a great dessert, hope you enjoy :)