Place ½ tablespoon of butter into each ramekin. Place the ramekins on a baking sheet and put in the oven for 5 minutes or until the butter starts to bubble. Carefully remove the baking sheet from the oven.

In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter, oil, and sugar on medium-high for 2 minutes until light and fluffy. Add the eggs and vanilla. Beat for 1 minute. Stop to scrape down the sides of the bowl if necessary. With the mixer on low speed, carefully add about half of the flour mixture and beat to combine. Add the buttermilk and beat to combine. Add the remaining flour mixture and beat to combine.

Pour the batter into the warm ramekins, filling each only 2/3 full. (You may have a little extra batter to fill an additional ramekin.) Bake the cakes for 20 minutes or until a toothpick inserted comes out clean.

Let the cakes cool for 10 minutes before removing from the ramekins. To remove, run a sharp knife around the inside edge of each ramekin. Working with one ramekin at a time, place a serving plate over the top of the ramekin and, while holding the plate in place, flip the ramekin upside down onto the plate. You may need to tap the ramekin once or twice to get the cake to release.

Serve the cakes with vanilla ice cream.