Preheat the oven to 350 degrees F. Spray a 12 cup Bundt pan with cooking spray.
Whisk together the flour, baking powder and salt in a medium bowl; set aside.
Beat the butter, sugar and oil in a large bowl with an electric mixer on medium-high speed until light in color and fluffy, about 5 minutes. Beat in the eggs, one at a time, and then the vanilla until combined.
Alternate folding in the flour mixture and the milk into the batter with a spatula, adding the flour in three additions and the milk in two, starting and ending with the flour, until just smooth. Divide the batter evenly into two medium bowls. Fold the cocoa powder into one bowl and mix until incorporated. Fold 1/2 cup peanut butter into the second bowl and mix until incorporated.
Use an ice cream scoop or large spoon and drop alternating scoopfuls of the batter into the pan. Drag a long wooden skewer through the batter, making sure the skewer reaches the bottom, to marble the colors in a tie-dye effect. Bake the cake until a skewer inserted into the center comes out clean and the center springs back when touched, about 40 minutes. Let cool in the pan for 10 minutes, then turn out onto a cooling rack and refrigerate to cool completely and chill, about 1 hour. Trim the bottom of the cake with a serrated knife so it will sit flat on a serving platter.
Meanwhile, microwave the chocolate and coconut oil in a medium microwave-safe bowl in 30 second intervals, stirring between each, until melted and smooth, about 1 minute. Microwave the remaining 1 3/4 cups peanut butter in a medium microwave safe bowl until warm and flowing, like lava, but still slightly thick, about 20 seconds.
Place the cooling rack with the chilled cake on it into a baking sheet. Pour the chocolate sauce over top of the cake letting it drip down the sides. Sprinkle the top with the peanuts. Let the chocolate harden, about 1 hour. Transfer the cake to a serving platter. Pour the peanut butter into the hole in the center of the cake. Cover the peanut butter completely with chocolate sprinkles. Serve immediately.
When measuring flour, we spoon it into a dry measuring cup and level off the excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)
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