First, heat-treat the white cake mix. Pour the cake mix into a microwave-safe bowl. Heat in the microwave in 30 second intervals, stirring in between, until the cake mix reaches 160℉ (71℃), approximately 1 to 1 ½ minutes total. Run the cake mix through a fine mesh strainer and set aside to cool.
Next, make the cake batter whipped cream. In the bowl of a stand mixer fitted with a whisk attachment or in a large mixing bowl with an electric hand mixer, whip the heat-treated cake mix, heavy cream, powdered sugar, and vanilla extract until medium peaks form. Fold in the rainbow sprinkles. Fill a large piping bag with the tip cut off with the whipped cream.
Line a cupcake pan with 24 cupcakes liners, two in each cup. Pipe a small amount of the cake batter whipped cream in the bottom of each liner.
Dip 12 of the Golden Oreos in milk and place one in each cup on top of the cake batter whipped cream, pressing down gently.
Pipe a layer of the cake batter whipped cream on top of the Golden Oreos until they are fully covered.
Dip another 12 of the Golden Oreos in milk and place one in each cup on top of the cake batter whipped cream, pressing down gently.
Pipe a final thick layer of the cake mix whipped cream on top of the Golden Oreos, extending slightly over the top of the cupcake liners. Spread the whipped cream evenly with an offset spatula.
Chill the funfetti icebox cupcakes for at least 12 hours.
Next, make the vanilla whipped cream. In the bowl of a stand mixer fitted with a whisk attachment or in a large mixing bowl with an electric hand mixer, whip the heavy cream, powdered sugar, and vanilla extract until medium-stiff peaks form. Fill a large piping bag fitted with a Wilton 1M piping tip with the whipped cream.
Pipe a generous swirl of whipped cream on top of each cupcake. Decorate with rainbow sprinkles and additional Golden Oreo cookies, if desired. I recommend adding the decorative Oreos and sprinkles until immediately before serving for best results.