Measure everything and line two baking sheets with parchment paper. Have a tablespoon or cookie scoop ready.

In a medium saucepan, combine the butter, sugar, and milk. Heat over medium, stirring frequently until the butter melts and the sugar dissolves.

Bring the mixture to a full rolling boil—large bubbles continuously breaking across the surface—and let it boil for 60 seconds without stirring.

Remove the pan from heat. Immediately stir in the peanut butter and vanilla until smooth and fully combined.

Add the quick oats and stir until every oat is coated and the mixture is uniform.

Drop rounded tablespoonfuls onto the prepared parchment, leaving a little space between each. Flatten slightly with the back of the spoon if you prefer thinner cookies.

Let the cookies cool at room temperature for 45 minutes to 1 hour until firm.

Once set, transfer to a plate or airtight container.