Whisk the egg yolks and sugar until light and pale. In a pan heat the milk and cream until nearly boiling, then pour over the egg and sugar mixture, whisking as you go.
Stir in the peanut butter and churn until frozen. Alternatively, put in a Tupperware tub and put in the freezer. Remove every half an hour or so and whisk to break up the ice crystals. Repeat until the ice cream is frozen.
To serve, remove from the freezer for twenty minutes or so to soften.