For a richer flavor, consider browning the roast in a cast-iron skillet before transferring it to the pressure cooker. Adjust the amount of mushrooms to your liking. Cremini or shiitake mushrooms work particularly well in this recipe. If you don't have fresh thyme, you can substitute with 1 teaspoon of dried thyme. Similarly, 2 dried bay leaves can replace the fresh ones. Serve the pot roast with mashed potatoes, creamy polenta, or crusty bread to soak up the delicious gravy.