In a large heavy-bottomed pot, melt the sugar, milk, butter, cocoa and cinnamon together over medium heat, stirring frequently
When melted, raise the heat to medium high, and when mixture comes to a gentle rolling boil, or starts bubbling, cook for one minute then remove from heat
Stir in the peanut butter, and when melted, stir in the oats and vanilla extract
When mixture is completely combined, drop by tablespoonfuls onto wax paper-lined baking sheets. Top with any extras at this point
Refrigerate until firm, and store in fridge
Notes
You can add shredded coconut, chopped nuts or candies to cookies before they firm up, if desired