Preheat oven to 325°F (DO NOT use convection). In a three-quart saucepan over medium heat, slowly warm
the milk just to a simmer. Add the sugar and whisk constantly until fully dissolved; do not allow the mixture to
boil (lower the temperature if necessary). Once the sugar is incorporated, add the chocolate and peanut butter
and continue to whisk until the liquid comes back to a simmer. Ensure the chocolate has fully dissolved,
but again, do not allow the mixture to boil. Remove from heat and add the vanilla. In a small bowl, whisk the
egg yolks together, then slowly whisk them into the chocolate mixture. Strain the final mixture through a fine
mesh sieve and into a two-quart liquid measuring cup to remove any residual lumps.
Pour the custard into (4) 10-ounce ramekins, 1/4 inch short of the top. Place the ramekins into a deep pan
and add enough boiling water to reach 3/4 up the sides of the ramekins. Bake until the custards are almost
set in the center, about 50 minutes. Remove from water bath and refrigerate until thoroughly chilled. Garnish
with a sprinkle of powdered sugar and a dollop of peanut butter if desired.