Add 1/4 cup of room temperature water to large glass measuring cup. Sprinkle plain gelatin over the water and allow it to bloom for 1 minute, making sure all of the powder gelatin is soaked in water. Boil water in the mean time.
After the plain gelatin has bloomed, add 3/4 cup of boiling water and the lemon Jello to the measuring cup. Stir until completely dissolve and set aside to cool down slightly. You’ll want to start working on the cream cheese mixture when the lemon gelatin is still slightly warm.
In a stand mixer bowl, whip the heavy whipping cream with the whisk attachment on medium-high speed to stiff peak, transfer to a smaller bowl and set aside.
In the same stand mixer bowl, cream sugar and cream cheese together with the whisk attachment on medium speed. Add the whipped cream back into the bowl and stir to mix the cream cheese and whipped cream together. Scrape the side and bottom of the bowl with a spatula to ensure thorough mixing.
With the mixer on stir, pour the slightly warm lemon gelatin into the cream mixture and mix until all the liquid has incorporated completely. Increase speed to low and mix until completely smooth. Scrape the side and bottom of the bowl with a spatula as necessary.
Pour this mixture on top of the cool crust and chill in the refrigerator for about 2 hours or until completely set.