Using an electric mixer with the whisk attachment whisk together egg yolks and sugar until thick and pale. Set aside.
In a saucepan over medium heat add the milk, cream, chocolate, and peanut butter. Stir continually until the chocolate has melted.
Remove from heat and slowly add the egg mixture, whisking constantly. Add vanilla. Return to heat and stir until smooth and thick enough to coat a metal spoon. Do not allow to come to a boil.
Refrigerate, covered, until thoroughly chilled, several hours or overnight.
Spread peanut butter inside the rim of serving glasses (easiest when using melted or warm peanut butter). Pour eggnog into glasses and serve with whipped cream, cinnamon, and nutmeg.