Once, years ago, a girlfriend was visiting me at the semiconductor test equipment mfg company I was consulting to while I was stuck late finishing some experiments. She grew restless and hungry, not being geek enough to find the test gear in and of itself interesting. The kitchenette was stocked with only the usual bad coffee gear--ultra-pasteurized cream cups, sugar packets, and bad coffee. I asked if she wanted some ice cream and she thought I was teasing.

I took one of the vacuum insulated coffee carafes from the kitchenette and filled it dramatically with LN2 from a roll-around 160 liter dewar in the lab (any time you crack the liquid feed on one of those things it's pretty dramatic with the hissing and the steam and the gurgling and the spattering, dancing beads of LN2). As an aside, vacuum insulated coffee carafes filled with LN2 will hold it for more than a day.

I carried it boiling and fogging back to the kitchenette as she followed at a more than safe distance. I found a plastic bowl in the sink and filled it with the contents of about 100 of those little ultra-pasteurized coffee creamers and about 100 packets of sugar, brewed up a fresh pot of coffee and skimmed the first few seconds worth off--when it actually has some flavor--and added it to the bowl. She looked mighty dubious, but the glass liner had cooled enough that the carafe didn't seem dangerous any more so she moved in to watch.

Then while I stirred the mixture with a plastic spoon (and, don't forget - while wearing the bright blue cryogenic safety gloves and full face shields) she poured in the LN2 which filled the bowl with dense fog that poured out, over the counter, and down around our ankles, spreading out across the floor, looking for all the world like a bad sci-fi movie.

In about 30 seconds we had a bowl of half decent coffee ice cream to share.
And, for just a little while, she thought being a geek was really cool...

This past weekend, I got to recreate the experiment, but with two gorgeous and technically oriented women who were were entirely up for dangerous fun in the kitchen. The updated recipe Carolyn, Joanne, and I came up with is:

1.5 cups 0.5 & 0.5
0.75 cups fine sugar
1.0 cup hot coffee (chilling it would reduce LN2 usage)
2.0 TSP ultra-fine ground coffee (turkish grind)
24oz (roughly) LN2 added from vacuum insulated all-stainless cups.

Mix ingredients for a while in the mixer, then slowly add the LN2. Don't add it too fast or it floats on the mixture and freezes the top solid. As it mixes in, the bowl will chill and soon the mixer will be straining against the ice cream, which is light and fluffy and has no detectable ice crystals.