Pour the milk or half and half into a 1.5 quart slow cooker.
Add the vanilla, powdered sugar, cocoa powder, peanut butter morsels, and chocolate chips. Whisk to combine.
Heat the cocoa on HIGH power for 1 to 1 1/2 hours, stirring every 30 minutes.
If not serving the cocoa right away, reduce the temperature to the warm or low setting until ready to serve.
Before serving, pour the steamy hot chocolate peanut butter cocoa into your serving mugs.
Add a generous helping of whipped cream on top of the cocoa. Sprinkle with the chopped Reese’s pieces. Drizzle the chocolate syrup and melted peanut butter on top. Add a Reese’s peanut butter cup.