Combine sugar, butter, milk, and cocoa in a saucepan over medium heat until they are a smooth liquid. Bring to a rolling boil; continue to boil for at least 1 minute.

Remove from heat and stir in chocolate-hazelnut spread and vanilla extract until dissolved. Return the pot to the still-warm burner, or the lowest setting on gas stove, and add oats. Mix well.

Leave the pot on the warm burner while you drop cookies by heaping spoonfuls onto wax paper. Let set and serve.