01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - Heat 2 tbsp olive oil in skillet over medium heat. Add chopped mushrooms and onion. Sauté 6–8 minutes until softened and moisture evaporates. Stir in garlic and cook 1 minute. Remove from heat and cool slightly.
03 - In large bowl, combine ricotta, cooled mushroom mixture, breadcrumbs, Parmesan, parsley, oregano, egg, salt, and pepper. Mix until well combined.
04 - Shape mixture into 16–18 golf ball-sized meatballs and place on prepared baking sheet. Bake 18–20 minutes, turning once halfway, until golden and set.
05 - While meatballs bake, heat 2 tbsp olive oil in saucepan over medium heat. Add onion and cook 4 minutes until translucent. Add garlic and cook 1 minute.
06 - Stir in crushed tomatoes, basil, oregano, sugar, salt, and pepper. Simmer uncovered 15–20 minutes, stirring occasionally, until slightly thickened.
07 - Gently transfer baked meatballs to sauce. Simmer together 5 minutes to meld flavors.
08 - Serve hot, garnished with fresh basil and extra Parmesan. Pair with spaghetti, polenta, or crusty bread.