Step 1In a nonstick skillet, heat the olive oil over medium-high heat until hot. Add the mushrooms and sauté, stirring constantly, until they have given up their liquid and it evaporates, and the mushrooms have begun to caramelize, about 5 minutes. Stir in the onion, celery, garlic and parsley, reduce the heat and continue to cook until the vegetables have softened slightly, 5 to 7 minutes. Remove from heat and set aside to cool. Meanwhile, heat the oven to 375 degrees.
Step 2In a large bowl, combine the ground pork and beef with the cooled vegetable mixture, fennel, red pepper, mushroom powder, bread crumbs, egg and salt, mixing until thoroughly combined. Set aside 2 cups of the meat mixture to use in the tomato sauce.
Step 3Form the remaining mixture into 12 meatballs, each roughly 2 1/2 inches in diameter. Place the meatballs on a parchment-lined baking sheet and bake until the meatballs are browned and cooked through, 15 to 20 minutes.
Step 1Heat the oven to 300 degrees.
Step 2Heat a heavy oven-proof pot or Dutch oven over medium-high heat until hot. Add the olive oil, then the onion, celery, garlic and parsley and stir for 3 minutes to marry the flavors. Add the meatball mixture and stir until lightly browned, about 3 minutes. Stir in the salt, sugar, pepper flakes and tomato paste and continue to cook for 2 minutes.
Step 3Stir in the canned tomatoes and bring the mixture to a simmer. Fit the lid over the pot and place the pot in the oven. Cook the sauce for 3 hours, stirring every hour or so. Remove from heat and stir in the fresh basil and oregano. Set aside until completely cooled. This makes about 2 1/2 quarts sauce, which will keep, covered and refrigerated, up to 1 week.
Step 4Before serving, gently reheat the sauce in the pot (this can be done on the stove top or reheated with the meatballs in a 300-degree oven for 20 minutes or so). Taste and adjust the seasoning if desired. Serve the sauce and meatballs over the spaghetti and garnish with grated Parmesan.