1 1/2 c heavy cream
6 large egg yolks
1 15-ounce can sweetened condensed milk
1/2 c key lime juice (fresh from 8-10 limes or used bottled key lime juice)
Bring the cream to a simmer in a heavy medium saucepan. Slowly beat the hot cream into the egg yolks in a medium mixing bowl. Pour the entire mixture back into the pan and place over low heat.
Stir constantly with a whisk or wooden spoon until the custard thickens slightly. Be careful not to let the mixture boil or the eggs will scramble.
Remove from heat and pour the hot custard through a strainer into a large bowl. Allow the custard to cool slightly, then stir in the sweetened condensed milk and key lime juice. Cover and refrigerate until cold or overnight.
Stir the cold custard well, then freeze in one or two batches in your ice cream machine according to the manufacturer's instructions.
When finished, the ice cream will be soft but ready to eat. For firmer ice cream, transfer to a freezer-safe container and freeze at least 2 hours.
Yields: about 1 quart