1 1/2 cups flour
1 1/2 tsp baking powder
1/4 tsp baking soda
1/4 tsp salt
1/4 cup butter, melted
1/4 cup vegetable oil
1 cup sugar, divided
3 eggs, separated
1/4 cup white or light rum
1/3 cup sour cream or yogurt
3 Tbsp chopped pecans or walnuts
Glaze
1/4 cup butter
2 Tbsp water
1/3 cup sugar
2 Tbsp rum
Grease a 6-cup bundt pan liberally with cooking spray. Add a few Tbsp of sugar and gently tap and turn to coat the entire inside of the pan. Spread the chopped pecans or walnuts in bottom.
Beat egg whites until soft peaks form. Slowly add 2 tablespoons of the sugar and continue beating until stiff and glossy. Set aside.
Whisk together flour, baking powder, salt, baking soda, and the other 3/4 cup sugar. In a separate bowl, beat the melted butter, sour cream or yogurt, rum, oil, vanilla, and egg yolks. Add the dry ingredients and beat just until smooth. Fold about 1/3 of the egg whites into batter to loosen it, then add the remaining whites and gently fold in until no streaks remain. Pour the batter evenly into the sugared pan.
Put 1 1/2 cups of water in the Instant Pot. Put the uncovered cake on a trivet into the pot, close the lid and set the valve to Sealing. Push Pressure Cook (or Manual) and adjust the time using the + and - buttons to get to 50 minutes. When it beeps that it's done, leave it for 10 minutes natural release.
Boil together the butter, water and sugar until dissolved. Remove from heat and allow to cool slightly. Add 2 Tbsp rum – be careful as it may boil up if it's too hot. Poke holes all over cake with a toothpick or skewer and slowly drizzle butter/rum syrup all over. Allow the cake to cool completely and serve with whipping cream.