• Position a rack in the lower third of the oven and preheat to 325°. Coat a 12 cup Bundt pan with nonstick cooking spray and dust it lightly with flour (I read recently that the best way to get a bundt cake out of a bundt pan whole was to brush melted butter over the pan and then dust it with flour. I tried this and for the first time I unmolded a PERFECT bundt cake.)
• Sift together flour, baking powder and salt into a large bowl.
• In the bowl of a stand mixer fitted with the paddle attachment, beat butter and vanilla extract on medium speed until smooth and creamy. (I thought this was NEVER going to happen but it finally did. Be patient with the ugly mess that it is until it comes together.)
• Add sugar and beat until evenly mixed, about 1 minute. Slowly pour in oil. Beat until light and fluffy, about 2 minutes. Add eggs and egg yolks, 1 at a time, beating thoroughly after each addition.
• Reduce mixer speed to low. Stir in flour mixture and buttermilk in three alternating additions, ending with the buttermilk, and continue to mix on low speed until batter is smooth and no lumps remain.
• Turn off mixer and fold batter several times by hand to ensure everything is well incorporated, and then pour batter into prepared pan.
• Bake for 60 – 70 minutes until the cake is golden, the top springs back when lightly pressed and a cake tester inserted into the center comes out clean. (Mine took 60 minutes). Place pan on a wire rack and let cool completely, about 2 hours.
• While the cake was baking I made my own marshmallow creme – just because. I needed to make two batches to make enough to have 7.5 ounces. One batch was around 5 ounces so there was some leftover for snacking. It is like eating vanilla air.

To Make the Vanilla Cream:

• Stir together the sugar, light corn syrup water and salt in a small saucepan over high heat. Boil, stirring occasionally, until it reaches 240°F.
• Place the egg whites and the cream of tartar in the bowl of a stand mixer with the wire whisk attached. Start whipping the whites to soft peaks at medium speed.
• The goal is to have the egg whites whipped and ready, waiting for your syrup to be drizzled in. If they’re whipping faster than your syrup is coming to temperature, just stop the mixer until the syrup is ready.
• When the syrup reaches 240°F, set the mixer to low and slowly drizzle a tiny bit of syrup, a couple of tablespoon’s worth, into the egg whites to warm them. (If you add too much they will cook and you will have one big mess). Slowly drizzle in the rest of the syrup and then increase the speed to medium high. Beat until the marshmallow creme is stiff and glossy, 7 – 9 minutes (I have made marshmallow creme many a time and I have never had it take this long. Usually for me it is around 4 minutes. I don’t know if it’s altitude or what); toward the end of the beating time beat in the vanilla.
• Use immediately or store in an airtight container.
• Now, back to the cake.

To make the filling:

• Beat together the marshmallow cream, softened butter and vanilla until well mixed. Transfer to a pastry bag fitted with a large, round hole.
• With the cake still in the pan, use a paring knife or an apple corer to cut 6 or 7 deep holes into the bottom of the cake, each about 3/4 of an inch in diameter; be careful not to cut through the top of the cake. Discard (ie: nibble) the cake scraps.
• With your fingers, gently burrow a horizontal tunnel around the center of the cake (I got a touch confused here. I have trouble with instructions like this as you will see. I am thinking it was not supposed to look like this, but it worked out in the end.) connecting the vertical holes.
• Insert the tip of the pastry bag and squeeze in filling, tilting pastry bag back and forth as you work to encourage filling into the horizontal tunnel through the cake. When cake is filled, use a spatula to scrape away excess filling from the bottom of the cake. (I forgot to take a picture of the filling. I covered the filling with cake scraps ’cause I thought I should since I really think I screwed up the whole tunnel thing.)
• Quickly and carefully invert cake onto a serving platter, Dust with confections’ sugar.