Preparation: Preheat your oven to 350°F (175°C). Generously grease and flour a 12-cup bundt pan, tapping out any excess flour.
Mix the Batter: In a large bowl, combine the cake mix, nut milk blend, 1/3 cup peanut butter, eggs, and vanilla. Beat with a hand mixer or stand mixer on medium speed until the batter is smooth and thoroughly combined.
The Mix-Ins: Gently fold in the peanut butter chips and mini chocolate chips using a spatula, ensuring they are evenly distributed.
Bake: Pour the batter into the prepared bundt pan. Bake for 45 to 55 minutes. Test for doneness by inserting a toothpick into the center; it should come out clean.
Cooling: Let the cake cool in the pan for exactly 15 minutes, then invert the cake onto a cooling rack or serving plate. Allow it to cool completely for several hours.
Make the Glaze: In a microwave-safe bowl, combine the 1 1/2 cups chocolate chips and 6 tablespoons of peanut butter. Microwave on high in 30-second intervals, stirring between each, until silky smooth.
Decorate: Pour the warm glaze slowly over the top of the cooled cake, letting it drip down the sides. Wait about 5 minutes.
The Topping: Sprinkle the chopped miniature peanut butter cups over the glaze, pressing them very gently so they adhere.
Set and Serve: Refrigerate the cake for at least 15 minutes to allow the glaze to set firmly before slicing.