Hit Sauté on the Instant Pot, add 1/2 tablespoon extra virgin olive oil, and let heat for about 1 minute.: As the oil warms you will notice a faint, glossy shimmer and a subtle scent of toasted olive; that signals the pan is hot enough for searing. This brief heating step primes the pot so the chuck roast makes steady contact and browns rather than steaming. If the pot is not hot enough you might not develop a crust, leading to a less flavorful final dish. A typical troubleshooting move is to pat the roast dry before searing, which reduces steam and improves browning.
While the oil is heating, season the chuck roast generously with kosher salt and pepper on both sides. Once seasoned, add the roast to the heated oil and sear the meat on each side, 3-4 minutes per side. Once the roast is browned and slightly caramelized, remove it from the inner pot, placing it onto a plate. Hit cancel to turn the Instant Pot off.: When searing you should hear an assertive sizzle and see a rich, deep brown color develop on the surface within minutes; that caramelization locks in savory notes. I like to rotate the roast to get even contact with the hot surface, and a proper sear also produces browned bits on the pot bottom that will boost the gravy. A common error is crowding the pot, which causes the temperature to drop and prevents searing, so work in a single layer or sear in batches.
Pour about 1/2 cup of the beef stock into the inner pot and scrape up any browned bits on the bottom of the inner pot using a wooden spoon or spatula.: Pouring a small amount of stock while the pot is still warm releases those caramelized bits, which dissolve into the liquid and become a flavor bomb for the braise. You will hear a soft sizzle as the liquid lifts the fond, and the color will deepen into a glossy brown. If you skip this deglazing step you risk a burnt on flavor and the Instant Pot may throw a burn warning, so always scrape thoroughly.
Add the seared pot roast back into the pressure cooker, along with any accumulated juices that collected on the plate. Pour the remaining beef stock around the roast. Season the broth with 1 teaspoon onion powder, 1 tablespoon minced garlic, and a generous pinch of salt and pepper. Spread 1/4 cup prepared horseradish over the top of the roast.: Reintroducing the roast to the liquid lets connective tissues begin to unwind as the pressure builds; you will notice a faint steam rising when you add the remaining stock. The aromatics will scent the broth quickly, and the horseradish on top creates a piquant layer that melts into the meat during cooking. A mistake here is undersalting the liquid, which results in a flat sauce, so season confidently but taste as you finish the gravy later.
Place the lid on the Instant Pot and ensure the vent knob is set to sealed. Select Manual or Pressure Cook, adjust to High Pressure if needed, and use the +/- buttons to set the cooking time. Cook for 20 minutes per pound.: As the pot reaches pressure you may hear the valve hiss softly and then settle; that is normal. The high pressure forces liquid into the meat fibers, breaking down collagen so the roast becomes tender enough to shred or slice. Accuracy with weight based timing matters because undercooking will leave the roast tough, while dramatically overcooking might make the meat too loose for neat slices. If you are uncertain about the roast weight, err slightly longer and allow for a natural release to finish tenderizing.
Once the cooking time has elapsed, allow for pressure to release for at least 15 minutes. Then open the inner pot, remove the roast, place it on a cutting board or platter, and tent with foil and let rest for while the vegetables cook.: Letting the pressure naturally release for a while helps the meat fibers relax gradually, retaining juices. When you lift the lid you will be greeted by a deep, braised aroma and a glossy broth. Resting the roast under foil keeps heat steady and allows juices to redistribute; slicing too soon will cause juices to spill out onto the cutting board, making the meat drier. People sometimes rush this step, so be patient and use the resting time to prepare vegetables for the next stage.
After removing the roast from the inner pot, add the prepared potatoes and carrots. Place the lid on the Instant Pot, ensure the vent knob is set to sealed, and using the Manual or Pressure Cook button, set to cook on high pressure for 5 minutes.: The vegetables will soften and absorb the savory broth quickly, and you should aim for tender but not falling apart texture. When you add them, the steam will look dense through the vent as it rebuilds pressure, and the pot will sing gently when cooking. A common slip is cutting potatoes too small which causes them to disintegrate under pressure, so keep the chunks about 2 inches for best texture.
After the cooking time has elapsed, let pressure release naturally for 5 minutes, then do a quick release of pressure by carefully knocking the venting knob from the sealed to the venting position using the handle of a long utensil. Stand back to prevent yourself from being burned by steam.: That short natural release lets the vegetables finish tenderizing without shock, then the quick release stops cooking so they hold their shape. You will see a rapid burst of steam and hear an energetic hiss during the quick release, so keep hands and face away. A safety note: always use a utensil to move the knob and keep your face to the side to avoid steam burns.
After the roast and vegetables are cooked, strain the cooking liquid from the inner pot and then return the inner pot to the instant pot.: Straining clarifies the broth and removes bits of sediment so your gravy finishes silky and smooth. The liquid will be richly flavored, with suspended particles that, if left, can cloud the sauce. If you skip straining the gravy may be grainy, so use a fine mesh strainer or cheesecloth for the best texture.
Hit Sauté on the Instant Pot and add 2 tablespoons unsalted butter. Once the butter has melted, whisk in 2 tablespoons all-purpose flour and then let cook for 1 minute.: As the butter melts it will foam briefly and release a gentle nutty aroma, which is the ideal foundation for a roux. Cooking the flour for a minute removes raw flour taste and develops a subtle toasty color that enriches the gravy. Stir constantly to prevent scorching; a burnt roux will ruin the sauce and is hard to recover from.
Slowly whisk in 1-2 cups of the leftover cooking liquid, whisking well. Let bubble and thicken for several minutes, whisking constantly. Serve with pot roast and vegetables.: Adding liquid gradually prevents lumps and helps you control thickness; a glossy, velvety sauce should cling slightly to a spoon. You will hear a gentle simmer as the gravy comes together, and the aroma will deepen into a concentrated roast essence. If the gravy becomes too thick, whisk in more strained liquid to loosen it; if too thin, simmer a little longer while stirring to reduce and intensify flavor.