Add the butter, sugar, & milk to a medium saucepan over medium heat. Bring to a boil and boil for EXACTLY one minute. (See notes.)
Remove the pan from heat, stir in the Nutella until blended together and smooth.
Add the oats, stirring until they are mixed in evenly.
Line 2-3 baking sheets (depending on the size you have) with wax paper.
Drop the cookies by rounded tablespoons evenly onto the wax paper.
Let the cookies sit at room temperature for 15-30 minutes until they are cooled and set.
Notes
If you boil the butter, sugar, and milk for less than 1 minute the cookies will not set up properly and will be sticky and wet.If you boil the butter, sugar, and milk for more than 1 minute the cookies will end up dry and crumbly.However, if you live in a humid climate, and it is very humid while you are making these cookies, boiling the butter, sugar, and milk for about 1 1/2 minutes is a good idea. The humidity in the air can make the cookies not set up properly as well. I live in Oklahoma and only when it is very very humid or raining outside do I have to boil for 1 1/2 minutes.
Since different foods are different sizes, nutritional facts are approximate and may not be exact but they are as close to accurate as I can calculate.