Spray a mini muffin pan with nonstick cooking spray, or like with mini cupcake liners. Set aside.
Preheat oven to 325°F (for nonstick or darker pans; for light pans, preheat to 350°F).
In a stand mixer with paddle attachment or in a large bowl using a hand mixer, mix together the brownie mix, melted butter and eggnog. Then beat in the eggs one at a time, just until all ingredients are well incorporated.
Scoop about one tablespoonful of brownie batter into each prepared mini muffin cup in the pan. Place in the oven and bake at 325°F for 25 to 30 minutes, or until a toothpick inserted into the center of a brownie comes out just about clean.
As soon as the brownies are fully baked, remove them from the oven. Then use the bottom of a large wooden spoon or the bottom of an ice cream scoop to gently poke a hole in the center of each mini brownie bite, taking care not to go all the way to the bottom of the brownies. Set aside to cool
Make the Eggnog Whipped Cream
While the prepped mini brownie bites are resting, in a large bowl, whisk or beat together the heavy whipping cream, eggnog, and confectioner's sugar for several minutes, until stiff peaks form.
Spoon the whipped topping into a pastry bag outfitted with a closed star pastry tip. Then pipe just enough whipped topping into each of the centers of the mini brownie bites. Sprinkle ground cinnamon over each and top with mini chocolate chips.
Notes
Brownie texture: If you like more cake-y brownies, let them bake towards the mid or end of the baking range in the recipe. If you like your brownies more moist, bake them for less time, around 24-25 minutes in this case.