Crack the eggs into the mixing bowl and whisk them together until they are well-beaten and frothy.
Pour the heavy whipping cream and water into the mixing bowl with the eggs, and continue whisking until the mixture is well combined.
Pour the custard mixture into custard cups or small ramekins.
Place the ramekins into a larger pan and fill the pan with near boiling water. Make sure the boiling water reaches halfway up the sides of the ramekins.
Bake for approximately 40-45 minutes in the center of the oven.
Check the custard. It should be slightly jiggly still, but not at all runny. If it appears too runny, cook a bit longer.
When you are happy with the consistency, remove the pan from the oven. Remove the ramekins from the water bath and allow the custard to cool.
Once cool, chill and store the custard in the refrigerator until ready to serve.
Video
Notes
Troubleshooting
If the keto custard isn't fully set or too soft for your taste, you didn't cook it long enough. You can remedy the problem by cooking the custard for a bit longer.
If your custard has many bubbles, or it separates and gets watery, it's likely because you cooked it at too high a temperature. Custard will curdle at temperatures above 185ºC/365ºF. Using a water bath around the custard cups ensures a consistent baking temperature and prevents curdling or separation of the custard. The water acts as an insulator and helps the custard cook gently and evenly. If you did use a water bath and still got separation, try lowering the baking temperature for your next batch
If you don't want a skin to form on top of the custard, consider covering the custard cups during the cooking process. Another option is to cover the pan with a lid and use the steam generated from the water bath to keep the custard surface from drying out.
Storage
When refrigerating custard, store it in an airtight container to avoid absorbing odors or flavors from other foods in the fridge. (Silcone covers like these work perfectly for ramekins and custard cups.) While it will store well for around a week, for optimal flavor and texture, consume your refrigerated custard within 3-4 days.
To freeze your custard, leave half an inch of space at the top of a freezer-safe container to allow for expansion during freezing. Cover the container with a lid, plastic wrap, or a beeswax wrap and place it in the freezer. Custard can be frozen for up to 2 months.
To thaw frozen custard, transfer it to the fridge and let it defrost overnight. If you are in a hurry, you can also thaw it by placing the container in a bowl of lukewarm water until it is defrosted. Avoid thawing custard in the microwave as it can cause it to separate or curdle.