In a medium mixing bowl, use an electric mixer to combine peanut butter and sugar until smooth. Add milk and mix on low until sugar is dissolved- a full two minutes. You don't want to be tasting crunches of sugar in your ice cream, so give it a chance to dissolve. Mix in heavy cream and vanilla and beat until well combined and smooth.
PROCESS THE ICE CREAM:
Turn on your ice cream machine, pour the base in the freezer bowl (make sure it has been in your freezer for 24 hours), and let mix until thickened, about 25 to 30 minutes. A couple of minutes before you're ready stop the mixing, add in the chopped peanut butter cups. The ice cream will be a soft-serve consistency. You can eat it right away, or freeze to eat later. If you freeze it for later, it will be more ice-cream-scoopable. Let it sit out for a few minutes before you try to scoop it.
*This recipe is GLUTEN FREE adaptable. If you're preparing this recipe as Gluten Free, make sure you use Reeses snack size or miniatures (those are known to be GF), and use a brand of peanut butter that is recognized as GF.
*Here's an easy way to measure sticky peanut butter: Just spray the measuring cups with nonstick spray before you spoon the peanut butter into them. It'll slide right out!
*Make sure you freeze your ice cream processor's freezer bowl for a full 24 hours before processing your ice cream.