Instant dry-ice ice cream (vanilla, with a chocolate variation)

Buy dry ice the day it will be used; do not touch it with bare hands, and work in a well-ventilated space.

Pulse the dry ice in a food processor to a fine powder, so no big chunks remain.

Stir together 4 parts cream, 2 parts milk and 1 to 2 parts sugar (1.5 used) by volume, with a splash of vanilla, just until the sugar is dispersed.

Pour a cup of base per serving into a big metal or plastic mixing bowl, larger than seems necessary.

Add the dry ice snow one spoonful at a time, beating it in with electric beaters (or a whisk); it bubbles up as the gas escapes. Too much at once locks it up solid.

Keep beating in spoonfuls, whipping in air, until it has a soft-serve texture. If it starts melting, add a little more snow.

For hard ice cream, transfer to the freezer overnight.

Variation: stir about a tablespoon of cocoa powder into a serving of re-stirred base, beat until dispersed, then beat in dry ice snow a spoonful at a time, breaking up any clumps of snow; stir in white chocolate chips. If it locks up, let it sit a couple of minutes to warm.