Heat oven to 400 degrees. Place bacon on a parchment paper-lined baking sheet. Bake for 10 minutes. Flip the bacon and bake for another five minutes. Check the bacon and if it needs more time, flip again and bake for another five minutes. Repeat until the bacon is cooked to your liking. Drain on a paper towel-lined plate and crumble when cool enough to handle. If you'd like to keep the risotto vegetarian, skip this step.
As the bacon bakes, bring the stock to a gentle simmer in a saucepan. Cover and keep warm. Measure and chop the other ingredients you'll use in the risotto.
In a separate saucepan or Dutch oven, melt 2 tablespoons of butter over medium heat and cook the onions until they're translucent, about four to five minutes. Stir in the garlic, nutmeg and cinnamon and cook for about 30 seconds.
Add the arborio rice and stir to coat with butter. If necessary, you can always add more butter. Cook for about two to three minutes.
Pour in the pumpkin ale and stir until most of the beer evaporates.
Adding one ladle at a time, pour in warm stock. Stir frequently until the rice absorbs all the stock. Add another ladle and repeat. While you want to stir most of the time, it's OK to take short breaks here and there.
After about 20 minutes, taste the rice to see how much it's cooked. When the rice is tender to your liking and the sauce is creamy, it's ready. If the rice is still too hard, keep adding chicken stock and continue to cook.
Once the risotto finishes cooking, turn off heat and stir in the Gruyere, pumpkin puree, fresh sage, remaining 2 tablespoons of butter and bacon if using. Keep stirring until the cheese and butter melts. If needed, add salt and pepper to taste.
Serve immediately. Enjoy!