To the liner of your Instant Pot, add the meatballs, broth, Dijon mustard, Worcestershire, allspice, nutmeg, onion, salt and pepper. Do not add the cream or flour in this step.
Secure the lid on your instant pot, and set to sealing.
Set to manual high pressure for 10 minutes. Add 2 minutes if using frozen meatballs.
Quick release the pressure. Ensure the meatballs are cooked to 165F.
Make the thickening slurry by mixing the flour and water together in a small bowl. Mix until no lumps remain. Then add the slurry to the pot.
Let the sauce sit for 2-3 minutes to cool just a bit, then stir in the cream. If you want a thicker sauce, add another round of slurry.
Serve on top of your side of choice. Rice, noodles, and spaghetti squash are my go to!