In a medium skillet, add in the chopped onions and olive oil. Cook on medium to medium-low until caramelized and brown, about 30-40 minutes. Stir occasionally and season with salt and pepper. Set aside to cool slightly.
In a large bowl, combine all of the meatball ingredients (half of your caramelized onions, the other half will go in the gravy). Stir gently until well combined. Form into equal sized meatballs using a scoop if you have one, and place onto a plate or sheet pan. You should get about 20-25 meatballs.
Preheat a large skillet on med-high heat. Drizzle with a little olive oil. Place meatballs into skillet and cook on medium until browned on one side, about 3-4 minutes. Turn meatballs over to cook on the other side, and cover. Cook for another 5 minutes. Monitor burner heat, if it seems too hot, turn it down. Stir occasionally to ensure meatballs are cooked on all sides.
Turn burner off, and remove meatballs onto a plate, leaving the cooking juices and bits in the pan to use for the gravy. In a microwavable safe dish, combine 2 cups chicken stock and bouillon cubes. Microwave in 1 minute increments, stirring in between, until the cubes dissolve. Use a fork to break them up in between microwave sessions. May take 2-4 minutes.
In a small bowl, dissolve the corn starch in the remaining 1/4 cup chicken stock, set aside.
In the same skillet used for the meatballs, return to burner on medium-high. Add in butter and chicken stock bouillon mixture. Whisk until butter is melted. Bring to a boil and whisk in the cornstarch slurry mixture. Make sure it comes to a boil, it will begin to thicken immediately, reduce heat to low. Whisk in onion powder, thyme, sage, and salt and pepper. Taste and adjust for seasoning. Stir in remaining caramelized onions. If gravy becomes too thick, add more stock. It will continue to thicken as it sits.
Add meatballs back into the gravy pan. Once meatballs are re-heated through, they are ready to serve. Serve over mashed cauliflower or potatoes. Or a combo of both!
Since the caramelized onions take a little while to make, you could make them the day before or even a couple days ahead. That way they're ready to throw in the meatballs and gravy and it cuts the recipe time down.
The fall flavors are in the gravy, however you could add the same herbs into the meatballs to really turn up the flavors of Thanksgiving and fall!