1. Prep the Vegetables

Finely mince 1 ounce of mushrooms and set them aside. Mince the onions.

2. Sauté the Onions

In the Instant Pot on sauté mode or in a skillet over medium-high heat, add 1 teaspoon olive oil and cook onions for 4–5 minutes until golden. Divide the onions into two equal portions.

3. Make the Meatball Mixture

In a large mixing bowl, combine:

• Half of the cooked onions

• Ground beef and ground turkey

• Chopped mushrooms

• Breadcrumbs

• Egg

• 1 tablespoon tomato paste

• ¼ cup beef broth

• ¾ teaspoon kosher salt and a dash of black pepper
  Mix gently until well combined.

4. Prepare the Sauce

In a small mixing bowl, combine the flour and 1 cup beef broth, whisking until the mixture is lump-free. Stir in the remaining onions, 1 tablespoon tomato paste, vinegar, Worcestershire sauce, and mustard powder.

5. Shape the Meatballs

Form the mixture into 20 small, evenly sized meatballs.

6. Choose Your Cooking Method

Stove Top

Warm the remaining teaspoon of olive oil in a large skillet over medium heat. Brown the meatballs for about 2 minutes per side. Add mushrooms, ⅛ teaspoon salt, a sprinkle of pepper, and the sauce. Cover and simmer on low for 25 minutes. Garnish with parsley.

Slow Cooker

Sear the meatballs in a skillet with the remaining teaspoon of olive oil, then transfer them to a slow cooker with mushrooms, salt, pepper, and sauce. Cover and cook on low for 6–8 hours.

Instant Pot

Using the sauté function, heat the remaining teaspoon of oil and brown the meatballs in small batches to avoid overcrowding. Add mushrooms, salt, pepper, and sauce. Secure the lid and cook on high pressure for 10 minutes. Release the steam—either quickly or naturally—and finish with a garnish of fresh parsley.