Step 1: Saut Aromatics: Turn the Instant Pot to the "Saut" setting. Add the olive oil and heat until shimmering. Add the chopped onion and cook until softened, about 3-4 minutes. Stir in the minced garlic, dried thyme, and dried rosemary, and cook for another minute until fragrant.
Step 2: Sear Chicken Thighs: Season the chicken thighs with salt and pepper. Add the chicken thighs to the Instant Pot and sear on both sides until lightly browned. This step enhances the flavor of the final dish.
Step 3: Pressure Cook: Pour the chicken broth into the Instant Pot, making sure to scrape up any browned bits from the bottom. Stir in the Dijon mustard. Cancel the "Saut" setting. Secure the lid and set the Instant Pot to "Manual" or "Pressure Cook" on high pressure for 10 minutes.
Step 4: Release Pressure: Once the cooking time is complete, allow the pressure to release naturally for 10 minutes, then perform a quick release of any remaining pressure.
Step 5: Thicken Sauce (Optional): If desired, remove the chicken thighs from the Instant Pot and set aside. Turn the Instant Pot back to the "Saut" setting. In a small bowl, whisk together the cornstarch and water to form a slurry. Pour the slurry into the Instant Pot and cook, stirring constantly, until the sauce thickens to your desired consistency, about 2-3 minutes.
Step 6: Serve: Return the chicken thighs to the Instant Pot to coat with the sauce. Garnish with fresh parsley and serve hot over rice, mashed potatoes, or your favorite side dish.
Optional Tips: For richer flavor, use bone-in, skin-on chicken thighs, but increase the cooking time to 12 minutes. You can substitute dried herbs with 1 tablespoon of fresh herbs, minced. To add vegetables, include sliced carrots and celery along with the onions in step 1.