Preheat the oven to 350 F. Place four cupcake liners into four separate wells of a cupcake tin, and spray the liners with baking spray. Fill the empty cupcake wells halfway with water. Set aside.
Whisk the dry ingredients (flour, sugar, cocoa, baking soda, salt, cinnamon) together in a medium bowl.
Mix the wet ingredients (bourbon, milk, maple syrup, cold coffee, vanilla, and vegetable oil) together in a larger bowl. Slowly whisk the dry ingredients into the wet ingredients until fully combined.
Divide the cupcake batter between the cupcake liners, and bake at 350 F for 15-17 minutes.
Allow the cupcakes to cool in the cupcake tin for five minutes. Transfer them to a wire baking rack, and allow to cool completely.
For the Topping ::
Finely chop the walnuts. In a small bowl, stir the walnuts, maple syrup, and cinnamon sugar together until completely combined.
Top the cupcakes each with chocolate frosting, then with at least a tablespoon of the walnut mixture. Add more frosting or walnuts as desired!