Start by beating the eggs, egg yolks, cream of tartar together. This will ensure a fluffy cake. Then add in the sugar, beat until all mixed, and the mixture has air bubbles.
Then mix in the liquid ingredients, buttermilk, melted butter, vegetable oil, and vanilla extract.
In another bowl mix the dry ingredients, cake flour, baking soda, baking powder, and the salt.
Then mix the two bowls together, the dry and wet, and make sure they are well combined, check the bottom for any dry ingredients not mixed into the batter.
Spray your Instant Pot Safe pan (See the detailed post about what pans will fit your Instant Pot)
Then pour the batter into the prepared pan.
Cover with foil, this will keep your cake dry.
If your Instant Pot came with a handled trivet: (when you first purchased it) put it on the bottom of a 6-quart or 8-quart Instant Pot. Make sure that the handles are up so that you can lift the cake out later.
If your Instant Pot did not come with a trivet or you can't find it. Then just use a small (OVEN, it has to be able to withstand heat) bowl turned upside down and placed in the center.
Place your cover on the Instant Pot. Make sure that the vent is on sealed
Cook on high pressure (manual) for 35 minutes. When the cooking time is complete, let the pressure naturally release.
Remove the cake carefully, making sure not to burn yourself, let the cake cool.
Remove the cake from the pan and frost it (if you would like to)
Plate, serve and enjoy!