How to Make It
Prepare the Roast: Set roast on a baking sheet or a plate; sprinkle roast all over with kosher salt. Let stand, uncovered, for at least 1 hour or up to overnight in refrigerator.
Stir together olive oil, pepper, granulated garlic, seasoning salt, and dry mustard to form a paste. Rub paste mixture all over roast. Set aside.
Set Instant Pot to Sauté on High; let heat 1 to 2 minutes. Place roast in hot Instant Pot.
Cook, turning to brown all sides, about 1 minute per side. Transfer seared roast to a plate. Cancel the Sauté setting.
Stir together sherry, water, fish sauce, and beef base in a small bowl; add to Instant Pot, stirring to combine with roast drippings in the pot. Add garlic, thyme, and bay leaf. Place steam rack in Instant Pot; set roast on rack. Seal lid on Instant Pot, and close release valve. Set to Low Pressure for 5 minutes, making sure the Keep Warm setting is also on. Press Start.
When timer is up for the 5 minutes of pressure, do not release pressure. Allow the Keep Warm setting to go for 35 to 40 minutes. Once that time is up, carefully release steam, and open Instant Pot. Insert a thermometer in thickest portion of roast to check temperature (115°F to 120°F for rare, 125°F for medium-rare, or 130°F for medium). If desired degree of doneness hasn’t been reached, replace and lock lid, add 8 minutes to the Keep Warm setting, and check again.
Transfer roast to a cutting board, and let rest at least 20 minutes up to 1 hour before thinly slicing.
Prepare the Jus: Strain roast drippings through a wire-mesh strainer into a bowl; discard solids. Rinse out the insert and return to base. Add beef broth and flour to drippings, and whisk until smooth; add to Instant Pot. Set the Sauté setting to medium heat. Cook, whisking occasionally, until jus is slightly thickened, about 5 minutes. Add salt and pepper to taste. Serve beef on sliced French bread with horseradish mayonnaise and Swiss cheese. Dip in Au Jus sauce.