Add the boiling water to a heat proof jug and sprinkle with gelatin. Use a fork or whisk to mix until dissolved. Set aside to cool slightly.
Meanwhile, add the cream cheese to the bowl of a food processor and blitz until creamy, 60 seconds. Scrape down the bowl and add the sweetened condensed milk. Blitz until well combined. Scrape down and add the zest of two lemons and the juice from the lemons (taking care not to get any seeds in the cheesecake mixture) and blitz until well combined.
Scrape down the bowl, add the yellow food gel (optional) and mix on high speed. While the mixer is on high speed, slowly pour the gelatin mixture into the food processor. Once it’s all in there, stop the mixer and scrape down for a final time. Mix for a final 30 seconds.
Pour the mixture on top of the biscuit base and place in the fridge to chill for 1 hour.