To make the ice cream, pour 1 cup of the heavy cream into a heat-proof bowl and nest inside a larger bowl filled with ice water. Place a fine mesh sieve over the top of both bowls.
In a saucepan, combine remaining heavy cream, milk, sugar, and salt. Cook gently over medium heat, stirring regularly, until sugar is dissolved and mixture just starts to steam. Remove from heat.
In a small bowl, whisk egg yolks. Slowly whisk in some of the warm cream mixture, 1/3 cup at a time, until about half of the cream mixture has been incorporated and yolk mixture is warm to the touch. You want to do this gradually; doing so will temper the egg yolks rather than cook them.
Pour yolk mixture back into the saucepan and return to medium heat, stirring constantly, until the mixture thickens slightly and coats the back of a spatula, about 5 to 7 minutes, or until it reaches approximately 165 to 170ºF. Do not allow it to boil.
Remove from heat, then add peanut butter and stir until smooth. Pour mixture through sieve into cold cream, discarding any solids. Add vanilla extract and stir until cool.
Cover mixture with plastic wrap, carefully pressing wrap down onto the surface of the cream mixture. This will prevent a skin from forming on top of the custard. Refrigerate until completely cool, at least 3 hours or overnight if possible.
Meanwhile, combine chocolate and peanut butter in a large, microwave safe bowl. Microwave on medium speed for 60 to 90 seconds, stirring every 15 seconds, until melted and smooth.
Fold in rice cereal until evenly coated. Spread mixture in a thin layer on a parchment-lined baking sheet, then freeze until firm. Just before using, coarsely chop into bite-sized pieces.
Churn ice cream according to manufacturer’s instructions. When ice cream is the consistency of soft serve, stir in the crunch pieces, then transfer to a freezer safe container and freeze overnight until firm.
