Beat together eggs and sugar in a large bowl with an electric mixer until thick, about 3 minutes. Set aside.
Step 2
Pour milk into a small saucepan and bring to a simmer over low heat. Gradually drizzle hot milk into egg mixture while whisking vigorously, then return whole mixture to the saucepan. Cook over low heat, stirring constantly, until thick enough to coat the back of a metal spoon. Do not boil.
Step 3
Remove from heat and whisk in peanut butter until smooth. Allow to cool slightly, then whisk in sweetened condensed milk, half-and-half, and vanilla until well combined. Cover and refrigerate until chilled.
Step 4
Pour mixture into an ice cream maker and freeze according to the manufacturer's instructions. Fold in peanut butter cups when mixture is still soft. Transfer to a container and freeze until solid.
