
Line two baking sheets with parchment paper and set them aside.
Add ½ cup salted butter, 1 ½ cups granulated sugar, and ½ cup milk to a large saucepan and heat over medium-high heat. While whisking, bring it to a rapid boil and whisk for one minute.
Remove it from the heat and immediately stir in 1 teaspoon vanilla extract, ¾ cup peanut butter, and 3 ½ cups quick oats until the peanut butter has melted and fully combined.
Use a large cookie scoop to immediately scoop the oat mixture onto the prepared baking sheets. Let the cookies sit until they have completely cooled and set up, about an hour.