Make the dry rub. Mix ingredients together in a small bowl. This will make more dry rub than you need. That is a good thing. You can use it on chicken, on pork chops… or on that other half of chuck roast in your freezer.
Season the chuck roast generously on both sides with the dry rub, rubbing it into the meat with your fingers.
Set your Instant Pot to sauté and let it heat for about a minute. Add the oil and let it heat for a moment. Brown the chuck roast on both sides until nicely browned, 4 to 5 minutes per side. Transfer to a plate.
Drizzle in more oil, if needed. Add onion and cook, stirring frequently, until it is slightly softened, 2 or 3 minutes. Add garlic and cook, stirring constantly, for about 45 seconds.
Turn off sauté function and add wine, broth and fish sauce to the pot. Using a wooden spoon, stir and scrape up browned bits—this will probably take some doing, but stick with it.
Return chuck roast to the pot, along with any accumulated juices. Add carrots and potatoes to the pot around the sides of the roast. Season lightly with salt and tuck the bay leaves into the liquid.
Seal the Instant Pot and set to pressure cook on high for 40 minutes. When it has cooked for the 40 minutes, let it do a natural release on its own for 10 minutes, then carefully turn vent to the venting release position. Allow all of the steam to vent and the float valve to drop down before removing the lid.
Transfer the pot roast to a serving platter and slice it across the grain. Discard the bay leaves and, using a slotted spoon, arrange the vegetables around the sliced roast.
At this point, you can quickly thicken the sauce using cornstarch and water, if you like (see Kitchen Notes). Or you can plate servings of roast and vegetables, and spoon the unthickened broth over them, which we did. Serve.