In a saucepan, melt the butter and then stir in the sugar. Add the milk, cocoa powder, peanut butter and vanilla and swirl until smooth.
Remove from heat and mix and fold in the oats.
Using a small spatula or large ice cream scoop, drop cookies into piece of wax or parchment paper. Let sit and harden for about 15 minutes before serving.
(If you can't wait the 15 minutes, I totally understand. Just know you'll have a 'cookie crumble' on your hands!)
Serve No Bake Peanut Butter Chocolate Cookies for dessert or snack.