Ballymaloe Vanilla Ice Cream

Beat the egg yolks until light and fluffy (keep the whites for meringues). Combine the sugar with 1 cup of water in a small heavy-bottomed saucepan. Stir over heat until the sugar is completely dissolved, then remove the spoon and boil the syrup until it reaches the "thread" stage, about 223-235 °F: it will look thick and syrupy, and when a metal spoon is dipped in, the last drops of syrup will form thin threads. Pour this boiling syrup in a steady stream onto the egg yolks, beating all the time by hand. (If you are beating the mousse in an electric mixer, remove the bowl and beat the boiling syrup in by hand; otherwise it will solidify on the sides of the bowl.) Add the vanilla extract or vanilla seeds and continue to beat the mixture until it becomes a thick, creamy white mousse. This is the stage at which, if you're deviating from this recipe, you can add liquid flavorings such as coffee. Fold the softly whipped cream into the mousse, pour into a bowl, cover, and freeze.