Preheat oven to 350°. Spray a 15x10-inch jelly-roll pan with baking spray with flour.
In a large bowl, whisk together cake mix, root beer, oil, eggs, cardamom, and allspice until smooth, about 2 minutes. Pour batter into prepared pan.
Bake until a wooden pick inserted in center comes out clean, about 20 minutes. Let cool completely.
In a large bowl, beat cream with a mixer at medium speed until thickened. Add confectioners’ sugar and vanilla; beat at high speed until light and fluffy. Spread frosting over cooled cake; sprinkle cake with peanuts.
Notes
*We used Betty Crocker White Cake Mix and Abita Root Beer.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/root-beer-float-sheet-cake/