In a small saucepan, melt the butter over medium heat. Stir in the brown sugar until it is moist. Spread in the bottom of your doughnut pan.
Sliced the drained pineapples in half into thinner rings. Place the rings in the doughnut pan and press into the brown sugar.
In the bowl of an electric mixer, beat the butter until it is creamy. Add the sugar and continue beating until fluffy. Add the egg and beat until it is fully incorporated.
In a separate bowl, whisk together the flour, baking powder and salt. In a measuring cup, stir in the vanilla into the buttermilk. Add the flour mixture in increments to the butter mixture, alternating with the milk. Beat until just combined.
Fill the doughnut pan about 2/3 full. Bake for about 18-20 minutes or until golden brown. Gently remove the doughnuts from the pan by inverting onto a plate.
Let it cool on a wire rack…or enjoy immediately.
Adapted from 1925 Winning Pineapple Upside Down Cake, Source Unknown and Best Baked Doughnuts Ever, Food.com.Pineapple Upside Down Cake Doughnut Tips
Canned pineapple rings need to be sliced in half into thinner rings -- this is critical not just for fitting into the pan, but also to provide the right pineapple to cake ratio in each bite. Just use a knife to carefully slice them in half!
Allowing the bake doughnuts for about 8 minutes, or until they easily pop out of the pan without breaking apart.
The doughnuts are delicious when eaten still warm, or can be cooled to room temperature and then enjoyed.
I highly recommend enjoying them freshly baked, but cooled doughnuts can be stored in an airtight container in the refrigerator for up to two days.