Lightly grease a 12-inch round pizza pan with a raised rim. For easier removal, line the bottom with a circle of parchment paper and lightly grease the parchment. Make sure your pan has a rim that can contain the batter. Do not use a completely flat pizza stone (I used a tart pan, because I couldn’t find my pizza pan!).

Prepare the brownie batter according to the package directions using the eggs, oil, and water listed on the box.

Pour the brownie batter into the prepared pizza pan. Spread it into an even layer, making sure the batter does not extend above the pan’s rim.

Bake according to the package directions for a similarly sized pan, beginning to check it at approximately 7 minutes early. I actually ended up baking mine about 5 minutes less than what I thought I would have to for the size pan I was estimating, so just make sure you’re watching. The brownie is ready when the edges are set and a toothpick inserted near the center comes out with a few moist crumbs.

Place the pan on a wire rack and allow the brownie to cool completely before adding ganache.

Place the semisweet chocolate chips in a heat-safe mixing bowl with the heavy cream. Microwave for 30 seconds and stir. Microwave for another 20-30 seconds and stir until the chocolate chips are completely melted into the cream. If you need to microwave for another 20-30 seconds, you can, it all depends on the strength of your microwave.

Allow the ganache to cool at room temperature for approximately 20–30 minutes, stirring occasionally. It is ready when it has thickened to a soft, spreadable consistency and no longer runs quickly from the spoon.

Spread the thickened ganache over the brownie, leaving a narrow border visible around the edge to resemble a pizza crust.

Use a knife to lightly mark the brownie pizza into 10–12 wedges. These lines will help you arrange the toppings and make the brownie easier to cut after decorating.

While the ganache is still soft enough for the toppings to adhere, decorate each section with fall-colored chocolate candies, candy corn and sprinkles.

Let the decorated brownie pizza stand at room temperature for 30–60 minutes, or until the ganache is set enough to slice. For especially neat slices, refrigerate it for approximately 15 minutes. Avoid chilling it for too long, since that can make the brownie and ganache overly firm.

Cut the brownie pizza along the marked lines using a plastic cake cutter (a knife might damage your pan). Wipe the knife clean between cuts for the neatest wedges. Serve at room temperature for the best fudgy texture.