Mix the egg with the heavy cream and cook in a small saucepan over low to medium heat, stirring constantly until you obtain a somewhat thick custard.
Remove from the heat, and allow to cool.
Mix in the milk kefir, vanilla extract, and honey to taste.
Chill the mixture.
Freeze in your ice cream maker, according to the directions for your particular machine.
When finished, transfer to another container and place it in the freezer for a couple of hours to harden it a bit more, giving it the consistency of ice cream.
Serve and enjoy!
If you are using granulated honey, consider adding the honey to the custard mix at the end of the heating process so that the heat will liquefy it again. If using liquid honey, add it with the kefir and vanilla extract while cool. Adding them to the cool custard helps retain the beneficial qualities of these ingredients.
Honey can be substituted with maple syrup, stevia liquid, or erythritol. The latter 2 will lower the sugar and carb count. Regular sugar can also be used, but it should be added to the cream and egg at the beginning so that the heat will dissolve the sugar crystals.
To make a vegan kefir ice cream, make kefir with coconut milk instead of dairy. Use coconut cream instead of whipping cream, and leave the egg out. Use one of the other sweeteners listed above. To make a fluffier ice cream, whip the coconut cream to incorporate air into it. Fold the other ingredients into the thickened whipped coconut cream.
This can be made without an ice cream maker. To make a no-churn frozen kefir, pour the finished mixture into a freezable container and place in the freezer. Remove from the freezer every 20-30 minutes, and mix the ingredients, scraping off the frozen mixture from the sides of the container and incorporating them into the rest of the mixture. Return it to the freezer, and repeat until you achieve the desired texture.
Once you have a frozen dessert of a "soft-serve" consistency, you can either serve it right away, or let it get a bit harder in the freezer. I have found it is best to move it to a new container before sticking it into the freezer. Not only does that help with not letting more ice crystals form, but it keeps your bowl free for a new flavor!
Store uneaten frozen kefir in the freezer. If it is too hard, soften it by removing it from the freezer for a little while before serving. (Around 30 minutes if stored in the fridge, or 10 minutes at room temperature.)