Been in the family for years. I made this as a kid at home.
While traditional baked cookies rely on flour matrices for structure, no-bake drop sweets depend entirely on sugar crystallization to hold their shape. Heat dissolves the sucrose completely into the milk, creating a supersaturated solution during the crucial one-minute boil. Cocoa solids and rolled oats disperse evenly through this hot syrup, absorbing moisture before cooling induces rapid sugar recrystallization. Dropping the mixture onto foil prevents sticking without requiring parchment paper.
Timing the boil precisely at 60 seconds ensures the sugar reaches the soft-ball stage concentration without scorching the dairy solids in the butter and milk. Undercooking the syrup results in runny drops that flatten on the tray, whereas overcooking produces a crumbly, dry mass that refuses to bind. Chill the shaped mounds at 40 degrees Fahrenheit for 15 minutes to accelerate fat solidification.