1medium yellow onionhalved lengthwise and cut into 1/2-inch slices
2cupslow-sodium beefor chicken broth
1lbcarrotspeeled and cut into 1-inch chunks
1lbwhole baby gold potatoesabout 10
Using a small, sharp knife make 6 to 8 (1-inch deep) slits in both the top and bottom of the rump roast and insert a sliver of garlic into each one. Liberally season the roast on all sides with salt and pepper.
Film the bottom of the pressure cooker with olive oil and heat over medium-high heat. Lightly brown the roast, 1 to 1-1/2 minutes on all sides and transfer to a plate. Drain any excess fat from the pan and add about 1 tablespoon more olive oil.
Add the onion to the pressure cooker and cook, stirring constantly, over medium-high heat until softened, 2 to 3 minutes. Deglaze the pan with about 1/4 cup of the broth, scraping up all the browned bits that have accumulated on the bottom of the pan.
Add the remaining broth along with the tomato paste and soy sauce. Combine well, then add the potatoes, carrots and remaining sliced garlic.
Nestle the beef roast into the center of the potatoes on top of the carrots and onion and if necessary, increase the heat slightly until the liquid starts to bubble.
Place the lid on the pressure cooker, lock it and follow the manufacturer's directions to set it for high pressure (15 psi).
Continue cooking until the cooker indicates that it has come to full pressure (ours took about 8 minutes on medium-high heat - 375°F).
Cook for about 5 minutes, then gradually reduce the heat on the cooker to medium, making sure that the pressure is maintained and that you still see steam escaping.
Cook for 1 hour from the time the cooker came to full pressure (see notes), then remove from the heat and allow the pressure to release naturally.
Transfer the roast to a carving board and tent loosely with foil while you prepare the gravy.
Using a slotted spoon, gently transfer the potatoes and carrots to a bowl, cover and set aside. Be careful if you want them to stay intact, they'll be very soft.
Strain the pan juices into a bowl and return the solids (onion and garlic) to the pressure cooker.
Transfer as much of the liquid as you can into a gravy/fat separator and set it aside for 5 minutes to allow most of the fat to rise to the top. Pour the defatted juices into a 2-cup measure and repeat the process to defat the remaining juices.
You should end up with about 2 cups of defatted juices. If not, you can add a little extra broth or even water. Add to the onion and garlic in the pressure cooker and bring the mixture to a boil over medium-high heat.
In a small bowl, whisk the cornstarch into 1/4 cup of water and add it to the boiling gravy. Continue cooking, stirring constantly, until the gravy is thick and smooth, 2 to 3 minutes (do not overcook). Transfer the gravy to a serving bowl.
Carve the roast into slices and arrange on a serving platter with the potatoes and carrots. Drizzle with gravy if desired and pass the remaining gravy at the table.
Note: Because most of the cuts of meat used for pot roast have large fibers, they have a tendency to shred when carving. If you have an electric carving knife, give it a try - we find it does a great job on this type of meat.
Tips for Making This Recipe
You can safely add an extra 7 to 8 minutes to the 1 hour cook time if your roast is at the higher end of the weight range (3-1/2 lbs).