1tsppure vanilla extract or vanilla bean paste(optional)
Combine the egg yolks, sugar, and salt in a bowl. Whip the mixture until it becomes thick and the color turns a light yellow.
Scald the milk in a pot, then gradually beat it into the egg mixture. If you add in too much too soon in will scramble your eggs. Take your time.
Place the bowl over a water bath or double boiler*. Continue to heat, sitrring constantly, until the mixture is thick enough to coat the back of a spoon. (Or 160°F.)
Immediately stir in the cold cream to stop the cooking. Add the vanilla if using.
Chill the mixture for at least 12 hours, then freeze in an ice cream maker according to the manufacturer's directions.
Place the ice cream in the freezer and freeze for 4 hours for a consistency similar to soft serve, or 12 hours for old-fashioned.
If you are using a container of heavy cream that has previously been opened, make sure to scald and cool it prior to use. This will help reduce the risk of food-borne illness.
To make a double boiler, you need a pot that can hold a bowl on top that is large enough to hold your custard base. Fill the pot with a couple inches of water, but not enough to touch the bottom of the bowl. Bring the water to a simmer and let the steam cook the contents of the bowl.
If you add the cold cream and vanilla at the same time, the heat from the custard base will cook out some of the impact of the vanilla. For the biggest flavor impact, add the vanilla at the end.