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["Position a rack in the lower third of the oven and preheat oven to 325u00b0F Coat a 12-cup Bundt pan with nonstick cooking spray and dust it lightly with flour.", "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. 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 to 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. Place pan on a wire rack and let cool completely, about 2 hours.", "Beat all filling ingredients together in a large stand mixer; transfer to a pastry bag with a large round tip.", "With the cake still in the pan, use a paring knife or apple corer to cut 6-7 deep holes in the bottom of the cake, each about 3/4"" in diameter, being careful not to cut through top of the cake.", "Discard cake scraps. With your fingers, gently burrow a horizontal tunnel around the center of the cake, connecting the vertical holes.", "Insert the tip of the pastry bag into each hole and squeeze in filling, tilting pastry bag back and forth as you work to encourage filling into horizontal tunnel through the cake. When the cake is filled, use a spatula to clear away extra filling from bottom of cake.", "Quickly and carefully invert cake onto a serving platter; sprinkle with powered sugar if desired."]
