Separate the egg yolks from the whites, and store/use the whites for another purpose.
Combine yolks with the honey, sugar, salt and nutmeg in a large mixing bowl and beat or use hand mixer until the mixture is smooth (no lumps) and turns a light yellow color.
Stir the kefir and heavy cream slowly into the egg mixture.
Dispense mixture into glass bottle (about one liter-sized bottle e.g.) that have tight-fitting bottle caps or swing top style lids. Tighten the lid.
Place bottle in the refrigerator to cure for 7 days. The nog will slowly but significantly thicken and build up pleasant carbonation as it cures.
Separation of ingredients during curing is normal, especially if you use unhomogenized or raw dairy (the cream really does rise to the top). Gently invert and rotate bottle as needed to reincorporate the nog ingredients until is consistent throughout the bottle. Do not shake the bottle!
Be careful when opening-- pressure can release slowly or quickly. It's best to open slowly over the kitchen sink, with the bottle over a bowl to catch any extra that spills over if the pressure is great.
For the best texture, let eggnog warm and expand slightly before enjoying. You should notice it getting nice and bubbly! It will be better and more unctuous than the richest cappuccino you've ever had. (This final step is worth waiting for!)
Store in refrigerator. Consume within 4 weeks.