Season both sides of the chicken breasts with salt, pepper, and Italian seasoning.
Select SAUTE on the Instant Pot.
Add half the butter and all the olive oil.
When hot, brown the chicken breasts in the Instant Pot.
Remove and set aside.
Add the remaining butter and olive oil and heat.
Sauté the mushrooms, shallot and garlic until the mushrooms and onions are soft.
Season with salt and pepper.
Add the chicken broth and deglaze the pot.
Press CANCEL on the Instant Pot to stop the sautéing process.
Transfer the chicken to the Instant Pot and secure the lid.
Set on MANUAL and cook for 10 minutes.
Naturally release the pressure for about 12 minutes.
Remove the lid and take out the chicken. Cover and keep warm.
Add the marsala wine and stir until combined.
In a large measuring cup, combine the cornstarch and water.
Whisk until smooth.
Pour into the Instant Pot.
Set the Instant Pot to SAUTE and stir until thickened.
Add the chicken back to the pot and cook for a few minutes until all is hot.
Serve immediately with a sprinkling of green onion as a garnish.’