Cake

1. Preheat oven to 325. Prepare a bundt pan by spraying with non-stick cooking spray or brushing with melted butter. Set aside.
2. In a medium bowl, stir together flour, baking powder and salt.
3. In the bowl of a stand mixer {or a large bowl}, beat together butter, vanilla extract and vanilla bean paste until smooth. Slowly pour in sugar until well combined and fluffy.
4. Add vegetable oil and beat until incorporated. One by one, add eggs and egg yolks, beating well after each addition.
5. Carefully add 1/3 of the flour mixture to the wet mixture, then 1/3 of the buttermilk, alternating until all of the flour and buttermilk is added. Mix until just smooth and incorporated.
6. Pour or spoon batter into prepared bundt pan evenly. Smooth out the top. Bake for 60 to 70 minutes or until the top is golden brown and a skewer or knife inserted in the center comes out clean.
7. Remove from oven and allow to cool for about 45 minutes to an hour before attempting to remove from pan. There have been many a bundt cake casualty from impatient bakers trying to flip over a still-warm bundt.

Filling

1. Beat all ingredients together until well mixed. Transfer to a piping bag with a round tip, or a zip top plastic bag with one corner snipped.

Assembly

1. This cake isn’t hard to assemble, but it is messy. Do yourself a favor and do this over a sheet pan so you don’t have cake crumbs all over your kitchen. The idea is to create 6 or 7 deep holes in the bottom of the cake. I find that the easiest way is to use an apple corer. Be careful not to poke all the way through the cake.
2. Once the holes are made, use the best kitchen tools you’ve got: Your hands! Burrow your fingers into the holes and create a tunnel from hole to hole. Do this carefully so you don’t split the cake. {Like I might have.} Carefully flip the cake over to clear the holes. Flip back over again and get ready to fill.
3. Using the marshmallow filling {you haven’t eaten it all yet, have you?}, stick the piping bag into each hole and squirt the filling in until you get some resistance. Don’t overdo it because, again, you can bust the cake open. We don’t want that. Make sure that the filling is getting into the main tunnel and not just each hole.
4. When you’ve used up all the filling, flip the cake over {carefully!!!} onto your serving dish. Sprinkle the whole bundt with powdered sugar before serving. Then sit back and watch your guests ooh and ahh over your surprise Twinkie cake.