Turn the Instant Pot onto saute mode and allow it to heat up. Add the oil. When hot, add the chicken pieces and brown on both sides, about 4 minutes total. Transfer the chicken to a plate.

Add the butter. When melted, add the onions and mushrooms. Saute until softened, about 3 minutes. Add the garlic and saute for 30 seconds.

Pour in the Marsala and deglaze the bottom of the pot. Bring to a boil for 3 minutes to burn off the alcohol. Pour in the chicken broth.

Turn off saute mode.

Add the Italian seasoning, salt and pepper. Stir to combine.

Add the chicken back to the pot pressing it down so it’s submerged in the liquid as much as possible.

Secure the lid and set the vent to sealing (if necessary for your model).

Set to cook on high pressure for 5 minutes. When done, allow a 10 minute natural release, then manually release remaining pressure.

Remove the lid and transfer the chicken to a plate. The sauce will be watery when you open the lid. That’s how it should be. Pour in the heavy cream.

Turn on saute mode. Mix together the cornstarch and water. When the sauce is bubbling, add the cornstarch slurry to the pot and stir until thickened.

Serve the chicken with the sauce poured over the top. It goes well with mashed potatoes or rice.