Preheat your oven to 350°F (or follow the temperature on your cake mix box). In a large mixing bowl, combine the cake mix, room temperature eggs, melted butter, and 1 1/4 cups milk. Mix until just combined—don't overmix, as this keeps the crumb tender. Pour the batter into a 9x13 inch baking dish and bake according to the package directions, usually 25-30 minutes, until a toothpick inserted in the center comes out clean. I always use Duncan Hines because it produces a noticeably moister crumb that holds up better when soaked with the pudding mixture.

Remove the cake from the oven and let it cool for 10-15 minutes—it should still be warm but not hot to the touch. Using a fork or skewer, poke holes every 2 inches across the entire surface of the cake, going about halfway down. In a medium bowl, whisk together the 4 cups milk and both packs of banana pudding mix until smooth and thickened, about 1-2 minutes. Pour about 3/4 of this pudding mixture evenly over the warm cake, using the back of a spoon to gently push it into the holes so it soaks throughout.

Refrigerate the cake for at least 1 hour so the pudding sets and the flavors meld. While the cake chills, warm the jar of vanilla frosting slightly—about 15-20 seconds in the microwave will make it pourable without melting it completely. In a small bowl, mix the remaining pudding from Step 2 with the warmed frosting and vanilla extract until smooth, then stir in the ground cinnamon for a subtle warmth that complements the banana and strawberry flavors. I like to add the cinnamon because it ties the flavors together beautifully without being obvious.

Remove the cake from the fridge and spread the frosting-pudding mixture evenly over the chilled cake. Arrange the sliced bananas and fresh strawberries on top in whatever pattern you prefer—I like to arrange them in a pattern so each slice gets both fruits. Serve immediately or keep refrigerated until ready to serve, as this cake is best enjoyed cold.