Prep: Preheat oven to 350°F (175°C). Grease and flour a 9 x 13-inch pan (or two 9-inch rounds).
Combine Dry Ingredients: In a large bowl, add the cake mix and 1 envelope of dry Dream Whip powder. Whisk to combine. Do NOT whip the Dream Whip separately here - it goes in dry.
Add Wet Ingredients: Add eggs, cold water, and vanilla. Beat with an electric mixer on low for 1 minute, then medium-high for 2-3 minutes until smooth and fluffy. The batter will look thicker and lighter than a regular box cake.
Bake: Pour into the prepared pan and bake for 30-35 minutes, until a toothpick comes out clean. The cake should spring back when touched.
Cool: Let the cake cool in the pan for 10 minutes, then transfer to a wire rack. Cool completely before frosting - a warm cake will melt the topping.
Make the Frosting: In a chilled bowl, combine 2 envelopes of Dream Whip, cold milk, vanilla, and powdered sugar (if using). Beat on high for 4-5 minutes until stiff peaks form.
Frost: Spread the frosting evenly over the cooled cake. Refrigerate for at least 30 minutes before serving to let it set.