Place half and half, sugar, and butter in medium saucepan. Cook over medium heat, stirring constantly, until sugar dissolves. Increase heat to medium-high and bring mixture to gentle boil. Remove pan from heat and add chopped chocolate and peanut butter, swirling pan to cover chocolate and peanut butter with hot half and half mixture. Let stand for about 3 minutes to melt chocolate and peanut butter fully. Gently whisk chocolate mixture until blended then stir in vanilla extract. Let stand at room temperature until cool.
Place heavy cream in medium chilled bowl. Whip cream until soft peaks form, using a hand mixer set at medium speed or a stand mixer. Fold whipped cream into chocolate mixture, then cover and chill or serve immediately.
Recipe by parsley sage sweet at https://parsleysagesweet.com/2009/09/27/the-real-puff-daddy-and-a-vols-au-vent-for-every-meal/