In a medium, heatproof bowl, whisk the yolks just to break them up. Set aside.
Uncover the cream mixture and put the pan back over medium-high heat. When the mixture approaches a bare simmer, reduce the heat to medium.
Carefully scoop out about ½ cup of the hot cream mixture and, whisking the eggs constantly, add the cream to the bowl with the egg yolks. Repeat, adding another ½ cup of the hot cream to the bowl with the yolks. Using a heatproof rubber spatula, stir the cream in the saucepan as you slowly pour the egg-and-cream mixture from the bowl into the pan.
Cook the mixture carefully over medium heat, stirring constantly, until it is thickened, cats the back of a spatula, and holds a clear path when you run your finger across the spatula, 1 to 2 minutes longer.
Stain the base through a fine-mesh strainer into a clean container. Set the container into an ice-water bath, wash your spatula, and use it to stir the base occasionally until it is cool. Remove the container from the ice-water bath, cover with plastic-wrap, and refrigerate the base for at least 2 hours or overnight.