Line 2 baking sheets with parchment paper and set side.
In a medium saucepan, heat butter, sugar, and milk over medium heat until mixture comes to a rolling boil (the entire surface should be full of vigourous bubbles.) Stir frequently while it is coming to a boil. Once you get a full rolling boil, set a timer for 60 seconds. Do not stir during this time period.
Once the 60 seconds is up, turn off the heat and stir in the peanut butter and vanilla until smooth.
Stir in the oats. Using a 1/4 cup measuring cup scoop up the dough and drop it onto prepared baking sheets. Press a few Reese's Pieces onto the top of each cookie.Tip- Do a test cookie. Dough shouldn't spread out too much, but if it does let the dough cool a minute or two before scooping out the remaining cookies.
Allow to set up for at least 30 minutes before serving.
Notes
Get all ingredients measured out and ready to go before you begin the recipe.