Get all of your ingredients ready and measured out. Line a baking sheet with baking mats or parchment paper and set aside.
Add the butter, sugar, and milk in a medium saucepan and heat over medium heat. Stirring often bring the mixture to a low boil for about 1-1/2 minutes.
Remove from the heat and add in the peanut butter and vanilla and whisk until creamy.
Add the quick oats to a large bowl and pour the peanut butter mixture over the top and mix until combined.
I like to use a 2 inch cookie scoop to drop spoonfuls onto the prepared baking mat you may need to gently spread then out a bit.
Let the cookies cool on the countertop until they set up or place into the fridge to speed things up.
Notes
Use quick cooking oats for the best chewy texture.
You need to make sure your mixture comes to a low boil and boils for at least 1 minute. This helps the cookies set up properly.
Store cookies in an airtight container at room temperature or in the fridge.