Trim outside fat from the beef roasts. In a small bowl combine thyme, coriander, salt, and pepper. Sprinkle about one-fourth of the seasoning on the top of one of the beef roasts. Select “sauté” on the instant pot; adjust to “normal” heat level if needed. Allow pot to heat for a couple minutes. Add half the oil.
Add the seasoned roast to pot seasoned side down (it will fit snugly and that's fine). Sprinkle some of the remaining seasoning mixture atop beef roast. Cook roast for 8 to 10 minutes or until well browned, flipping roast once about halfway through cooking. Remove roast from the pot; set aside.
Add remaining oil to the pot. Repeat seasoning and browning the second roast in the pot, using the rest of the seasoning mixture. Remove roast from the pot; set aside. Carefully pour whiskey into pot. Cook and stir until whiskey is boiling, scraping the browned bits from the bottom of the pot. Once most of the browned bits are released, press the “cancel” button.
Add 1 cup water and the onion wedges to the pot. Stack beef roasts atop onion wedges in pot. Lock instant pot lid in place; make sure the vent is pointed toward “seal”. Select “manual” on high pressure and adjust the time to 95 minutes. The pot will automatically start the cooking process and once the pot is up to pressure, the time will start to count down.
When the cook time is complete, select “cancel” and allow the pressure to release naturally. Once the pot is depressurized, remove the lid. Serve meat topped with some of the cooking juices and onion wedges, if desired.