Peel of 2 lemons
Fine granulated sugar
In a saucepan scald 3 cups milk with the peel of 2 lemons. Cover the pan, let the peels infuse for 20 minutes, and remove and discard them. In a large metal bowl set over a pan of hot water whisk together 4 egg yolks and 3 1/2 tablespoons fine granulated sugar with a large whisk until the mixture forms a ribbon when the whisk is lifted. Add 3 1/2 tablespoons sugar syrup and the hot milk in a stream, whisking constantly, and stir in 1/2 cup rum. Divide the mixture among 4 glasses or cups.