1. Make the Meatball Mixture

1. In a large bowl, combine the ground chicken, breadcrumbs, beaten egg, Parmesan, minced shallot, garlic, salt, and pepper.
2. Using your hands or a fork, mix gently until just combined—overmixing can make the meatballs tough.

2. Shape and Brown the Meatballs

1. Scoop the mixture by rounded tablespoonfuls (or use a small ice-cream scoop) and roll into uniform balls, about 1½ inches in diameter. You should end up with around 16 meatballs.
2. Heat 1 tablespoon of olive oil in a large skillet over medium heat.
3. Add half the meatballs, spacing them evenly, and cook for about 4 minutes, turning occasionally, until browned on all sides. Transfer to a plate.
4. Add the remaining tablespoon of oil and brown the second batch, then set aside with the first.

3. Prepare the Mushroom Sauce

1. In the same skillet (no need to wipe it out), add the chopped onion and sliced mushrooms. Sauté for 5–7 minutes, until the onions are translucent and the mushrooms release their liquid and begin to caramelize.
2. Sprinkle the flour over the vegetables; stir continuously for about 1 minute to cook off the raw taste.
3. Gradually pour in the chicken broth, stirring to dissolve any lumps. Scrape up any browned bits from the bottom of the pan—those add flavor!
4. Stir in the cream, Dijon mustard, and thyme. Bring to a gentle simmer and let the sauce thicken slightly, about 2–3 minutes.

4. Finish Cooking

1. Return the meatballs to the skillet, nestling them into the sauce.
2. Cover and reduce heat to low. Simmer for 8–10 minutes, or until the meatballs register 165 °F (74 °C) internally and the sauce is rich and creamy.
3. Give the sauce a taste, then add more salt and pepper if needed.