Heat the oven according to the temperature specified on the cake mix box and coat a 9x13 inch baking dish with non-stick spray or line it with parchment paper. Prepare and bake the cake following the directions on the package, checking a minute or two early to keep it moist while ensuring it's fully cooked.

Around 5 minutes before the cake finishes baking, combine the gelatin powder with the boiling water in a heat-safe measuring cup or bowl. Stir continuously for 2 minutes until the powder dissolves completely and the liquid turns clear. Let it cool briefly so it remains warm but not scalding.

Once the cake comes out of the oven, wait 5 minutes before proceeding. Use a fork or wooden skewer to create holes throughout the entire cake surface, placing them approximately 1 inch apart and pushing down about three-quarters of the depth. Gradually drizzle the warm gelatin mixture over the cake, pausing between pours to let it absorb into the holes rather than pooling on top.

Move the cake to the refrigerator and let it chill for a minimum of 4 hours until the gelatin has completely firmed up and no longer jiggles when touched.

In a mixing bowl, combine the softened butter and room-temperature cream cheese. Using a hand or stand mixer on medium speed, whip them together for 2-3 minutes until the mixture becomes pale, airy, and fluffy. Stop halfway to scrape the bowl sides. Add the vanilla extract and sea salt, then beat for an additional 30 seconds to incorporate fully.

Using an offset spatula or the back of a spoon, spread the cream cheese frosting in an even layer across the chilled cake, moving swiftly to prevent the frosting from warming up. Place the frosted cake back in the refrigerator and chill for at least 2 additional hours before slicing to allow the frosting to firm up and the flavors to meld together.