Boil the diced nopales until soft, then drain and rinse.
Blend the cooked nopales in a blender or food processor until smooth. Add a teaspoon of water if needed.
Combine the grapefruit juice, milk, heavy whipping cream, half the sugar, salt, and sriracha in a saucepan and bring to a boil over medium heat, whisking intermittently.
While heating, combine the egg yolks and the other half of sugar in a bowl and whisk to combine.
When the milk mixture has come to a boil, pour ⅓ of it into the egg mixture and stir. Then pour another ⅓ and stir, and then the final ⅓ and stir.
Next, pour the entire mixture back into the saucepan and heat, stirring constantly for 2 minutes, but do NOT let it come to a boil.
Then, using a sieve, transfer the mixture to a clean bowl, allow it to come to room temperature, and then refrigerate for 1-2 hours.
Optional: Add 1-2 Tbsp tequila to mixture and stir before refrigerating.
Optional: Add 6-9 drops green food coloring if you could like ice cream to be greener in color.
After the mixture is chilled, follow the manufacturer's instructions on your ice cream maker to make it into ice cream.
Transfer ice cream to a freezer safe container and freeze overnight to further harden.
In sandwich bags, melt the pink and yellow candy melts according to the manufacturer’s instructions and draw little pink flowers with yellow centers onto parchment paper. Allow to harden, then peel off and set aside.
To make the cactus ice cream cones, top an ice cream cone with one scoop of ice cream, poke with a handful of white jimmies sprinkles, and top with a candy melt flower.