Whisk together the milk, heavy cream, sugar, corn syrup, salt, and cornstarch.
1 ¾ cups whole milk, 1 ¼ cups heavy cream, ¾ cup granulated sugar, 2 tablespoons light corn syrup, 1 teaspoon kosher salt, 1 ½ tablespoons cornstarch
Place over medium-high heat, stirring occasionally until the mixture starts to steam. Continue to whisk and bring the mixture to a boil. When boiling throughout, remove from heat. Pass through a strainer if needed.
Pour into an airtight container and chill for 8-10 hours. While chilling, prepare peanut butter pieces.
For the peanut butter pieces
In a bowl, combine the peanut butter and powdered sugar.
½ cup smooth peanut butter, 1 ¼ cups sifted powdered sugar
Using a fork or pastry cutter, combine the two until small ball-like pieces form. If the mixture is too wet, add more sugar.
Store in an airtight container until ready to use.
To assemble
To freeze, remove it from the refrigerator and pour it into the ice cream freezer. Follow the directions with your freezer; each one can vary. My KitchenAid stand mixer (affiliate link) with ice cream maker attachment(affiliate link) takes about 20-25 minutes to freeze fully.
When finished, fold in the prepared peanut butter pieces and ½ cup dry roasted peanuts.
Transfer to an airtight container and place in a deep freeze for an additional 4-6 hours until hardened.