For the crust: Preheat the oven to 350 degrees F. Spray a 13-by-9-inch glass baking dish with cooking spray.
Combine the cake mix, vanilla and eggs in the bowl of an electric mixer fitted with the paddle attachment. Beat on medium speed until smooth, about 1 minute. Add the butter and mix just until combined. Spread the mixture evenly in the prepared baking dish.
For the filling: Dollop the jelly over the cake batter and smooth to the edges with an offset spatula. Beat the peanut butter and cream cheese in a clean electric mixer bowl with the paddle on medium speed until light and smooth, scraping the sides occasionally, 1 to 2 minutes. Add the vanilla and eggs and beat until smooth. Add the confectioners' sugar and beat on low speed to incorporate, and then beat on medium until light and smooth, about 1 minute. Pour over the cake layer and smooth the top with an offset spatula. Sprinkle with the peanuts.
Bake until the edges are puffed and golden brown and the center is just set, 35 to 40 minutes. Let cool.
For the glaze: Melt the butter in a medium microwave-safe bowl in the microwave. While the butter is still hot, whisk in the peanut butter until smooth. Whisk in the confectioners' sugar until smooth. Put the grape jelly in a small microwave-safe bowl and microwave just until you can whisk it smooth, only about 15 seconds (don't melt it completely). Put the peanut butter glaze in a small resealable plastic bag and the jelly in another. Snip off a corner of each with scissors and drizzle the glazes all over the cake. Cut into squares to serve.
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