Warning: LN2 is ridiculously cold (it is at its boiling point of 77 K, or nearly 200 degrees Celsius below zero) and hence is inherently dangerous. Do not try to ingest it. Make sure anyone around LN2 understands its perils (Material Safety Data Sheet). Drunks should be kept well away. Do not attempt to confine it. I strongly recommend using a thick-walled polystyrene container to hold it in while making the ice creams; definitely do NOT use a cheap glass-walled vacuum flask: there is an appreciable probability of it cracking and imploding, which trust me, is utterly indistinguishable from exploding.
Step 1: You will need...
- popsicle sticks
- half-and-half cream
- vanilla flavoring (or whatever you happen to like)
- food coloring
- a few liters of liquid nitrogen (obtainable from a supplier like Praxair or Airgas, if you have a dewar to hold it in)
Step 2: Make ice cream mix
Whisk 5 egg yolks with 125 g of sugar until thick and creamy. Add to a large saucepan with 500 ml of half-and-half milk/cream, and stir over moderate heat for about 10 minutes, stirring constantly. Remove from heat and whisk again. Add flavoring (we used a teaspoon of vanilla essence) and coloring and put in refrigerator until ready to serve.
We made 2 batches of this and divided it into three jars (red, blue and uncolored cream).