1. Prepare and Bake the Cake:

• Preheat the oven according to the package directions on the vanilla cake mix.
• Grease and flour a 9×13 inch cake pan (or use baking spray with flour).
• Prepare the cake batter according to the package directions, using the ingredients listed on the box.
• Gently stir in 1/4 cup of rainbow sprinkles into the finished batter.
• Pour the batter into the prepared cake pan and spread evenly.
• Bake the cake according to the package directions, or until a toothpick inserted into the center comes out clean.

2. Cool and Poke Holes:

• Let the cake cool completely in the pan on a wire rack. This is important; poking a warm cake can make it crumble.
• Once cool, use the handle of a wooden spoon, a thick chopstick, or a similar tool (about 1/2 inch wide) to poke holes evenly all over the top of the cake. Poke down almost to the bottom, but not quite through.

3. Prepare and Add First Pudding Layer:

• In a medium bowl, whisk together one box of the instant pudding mix with 1 ½ cups of milk.
• Whisk just until it begins to thicken but is still quite runny and pourable (this happens quickly with instant pudding).
• Immediately use a small-tipped piping bag or a small spoon to carefully fill the holes in the cake with this pudding mixture.
• Spread any remaining pudding thinly over the entire top surface of the cake.

4. Prepare and Add Topping Layer:

• In the same (or another) medium bowl, mix the remaining box of instant pudding with the remaining 1 cup of milk.
• Whisk just until it begins to thicken (it will be thicker than the first batch).
• Gently fold the thawed frozen whipped topping into this thicker pudding mixture until well combined and fluffy.

5. Frost the Cake:

• Spread the whipped topping mixture evenly over the cake.
• If you wish, reserve some of the topping to pipe decorative swirls on top later.

6. Decorate and Chill:

• Decorate the top of the cake generously with extra rainbow sprinkles.
• If you reserved some topping, pipe swirls or dollops now.
• Refrigerate the cake for at least 30 minutes to allow the pudding layers to fully set before slicing and serving.

7. Serve:

• Slice and serve chilled.