Turn on the sauté function in the Instant pot. Once hot, add 1 tablespoon oil.
2 tablespoons cooking oil
Mix flour with a little salt and pepper in a shallow bowl. Dredge the chicken in the flour mixture, then place in the hot Instant Pot. Cook 2-3 minutes each side, then remove to a bowl.
¼ cup flour, salt and black pepper, 1 ½ pounds chicken
Add the second tablespoon of oil to the Instant Pot and add the onion and celery. Allow to sauté for 4-5 minutes, stirring occasionally.
1 onion, 2 celery ribs
While the onion and celery is cooking, cut the chicken into bite-sized pieces.
When the onion looks slightly translucent, add garlic to the Instant Pot and stir briefly. Then add the potato, carrot and diced tomatoes with juice. Deglaze the pot briefly by stirring and scraping to work up all the browned bits of flavor on the bottom.
2 garlic cloves, 1 pound potato, 2 medium carrots, 14.5 ounce can diced tomatoes
Add chicken broth, balsamic vinegar, the chicken pieces, and all the spices: rosemary, thyme, marjoram, salt, and bay leaves.
2 cups chicken broth, 1 tablespoon balsamic vinegar, 1 sprig fresh rosemary, 1 teaspoon dried thyme, ½ teaspoon dried marjoram, 2 teaspoons salt, 2 bay leaves
Cover, close and seal the Instant Pot. Set the cycle for meat/stew, 15 minutes at high pressure.
When the cook cycle is done, allow the Instant Pot to natural release pressure for 5 minutes, then quick release the rest.
Open the Instant Pot and set the function to sauté.
Mix the cornstarch with water to make a slurry. Add the frozen peas and the cornstarch slurry to the stew.
3 tablespoons cornstarch, ⅓ cup water, ½ cup frozen peas
When the mixture starts to boil, it will thicken from the cornstarch. If you want it thicker, you can repeat the cornstarch step or mash a few of the potatoes.