Line a baking sheet with parchment paper or a silicone mat.
In a medium saucepan over medium heat, add the cubed unsalted butter. Allow it to melt completely, stirring occasionally.
Once the butter is melted, stir in the granulated sugar, milk, and unsweetened cocoa powder. Keep stirring until the mixture comes to a rolling boil. Let it boil for 1 minute without stirring.
After boiling, remove the saucepan from heat. Stir in the chunky peanut butter, pure vanilla extract, and a pinch of sea salt. Mix until everything is well combined and the peanut butter is fully melted.
In a mixing bowl, combine the quick-cooking oats and toffee bits (if using). Pour the chocolate mixture over the oats and mix thoroughly until all the oats are coated.
Using a spoon or cookie scoop, drop heaping tablespoons of the mixture onto the prepared baking sheet. If desired, sprinkle a little sea salt on top of each cookie.
Let the cookies sit at room temperature for about 30 minutes or until they firm up and are easy to handle.
