Prepare Your Base: Add the diced onion, minced garlic, tomato sauce, water or broth, Worcestershire sauce, and seasonings to the Instant Pot. Stir everything thoroughly to create a smooth, cohesive sauce.

Add Meatballs: Gently place your frozen meatballs into the sauce mixture, trying to arrange them in a relatively even layer. Don't worry if they're slightly stacked—the pressure cooking will ensure they all cook through properly.

Seal and Cook: Secure the Instant Pot lid and ensure the pressure valve is set to "sealing." Select the Manual or Pressure Cook function and set to high pressure for 8 minutes. (If using particularly large meatballs, you may want to increase to 10 minutes.)

Quick Pressure Release: Once the Instant Pot finishes cooking, carefully switch the valve to “venting” for a quick release. Be sure to stand back—hot steam will escape quickly. Once the pressure pin drops, it's safe to open the lid.

Final Touches: Gently stir the meatballs and sauce. If the sauce seems too thin, you can select the Sauté function and simmer for 2-3 minutes to reduce, or add a cornstarch slurry to thicken.

Start Your Base: Set your Instant Pot to Sauté mode and melt the butter to begin. Add the diced onion and cook until translucent, about 2-3 minutes.

Build Flavor: Add the beef broth, Worcestershire sauce, nutmeg, allspice, salt, and pepper to the pot. Stir everything thoroughly and bring the mixture to a gentle simmer.

Add Meatballs: Turn off the Sauté function. Carefully add your frozen meatballs to the hot liquid.

Pressure Cook: Secure the lid, set the pressure valve to "sealing," and select Manual or Pressure Cook on high pressure for 8 minutes.

Quick Release and Finalize: When cooking completes, perform a quick release. Once safe to open, select the Sauté function again. Stir in the heavy cream and cornstarch slurry. Let it simmer for 2–3 minutes until the sauce thickens to your preferred texture. Finish with fresh chopped parsley.