Begin by preheating your oven to 350 degrees F and coating a 12-cup bundt pan with nonstick cooking spray. In a medium bowl, combine 2 cups all-purpose flour, 1/2 cup unsweetened cocoa powder, 1 (3 1/2 ounce) box chocolate cook-and-serve pudding and pie mix, 1 tablespoon baking powder, and 1/2 teaspoon salt.
In a separate large bowl, beat together 3/4 cup butter and 1 1/2 cups granulated sugar until the mixture becomes light and fluffy, approximately 2 minutes. Add 3 eggs one at a time to the butter mixture, beating well after each addition to guarantee proper incorporation.
Alternately add the flour mixture and 1 cup milk to the egg mixture, starting and ending with the flour mixture. Stir in 2 teaspoons vanilla extract, then pour the batter into your prepared bundt pan.
Bake the cake at 350 degrees for 46-50 minutes, or until it springs back when lightly pressed. Allow the cake to cool in the pan for 15 minutes before removing it to a wire rack to cool completely. While the cake cools, prepare the chocolate glaze by placing 6 tablespoons heavy cream in a small saucepan and bringing it just to a boil over medium heat, about 3 minutes.
Remove from heat and add 1 (6 ounce) package semi-sweet chocolate chips, stirring until completely melted and smooth. If needed, return briefly to low heat. Spoon the chocolate glaze over the cooled cake and allow it to set.
For the finishing touch, combine 3 ounces white baking chocolate (broken apart) and 1 teaspoon vegetable oil in a small microwave-safe bowl. Microwave for approximately 1 minute, stirring halfway through, until the mixture is melted and smooth.
Allow the white chocolate mixture to cool for 5-10 minutes, then drizzle it decoratively over the chocolate glaze and let the entire cake set completely before serving.
