Put roast in a large pot that has a lid.  Brown the roast at 375 degrees for about 30-45 minutes, without the lid. 
Then cut 1 inch deep slices across the top every 1 1/2 inches or so.  (Neither of those measurements has to be exact; that just gives you a general idea.)
Next sprinkle one packet of dried onion soup mix over the top, or you can use seasoning salt and pepper if you prefer. 
Peel potatoes and cut into chunks.  Put them and the carrots around the roast, and sprinkle with salt and pepper.  Peel the onion and cut it in half and then slice it thinly.  Place over the roast and other veggies.  Put two beef boullion cubes in.  Pour 1 1/2 cups of water into the pot.  Put lid on pot, and lower oven temperature to 300.  Cook for about 3-4 hours– while you are at church is fine. 
When you get home, take the pot out of the oven, and carefully put the vegetables in a bowl or serving platter, using a slotted spoon.  Put the meat on a cutting board and slice thinly.  Cover meat and vegetables to keep them warm. 
Pour liquid left in pot through a strainer into a glass measuring cup.  You want to have about two cups of liquid.  Put it back into the pot and bring it to a boil.  Mix together 1/2 cup water and 1/4 cup cornstarch in the measuring cup.  Once the liquid has come to a boil, slowly pour the cornstarch mixture in, stirring constantly.  Reduce heat to medium and keep stirring until it boils again.  Stir and cook until gravy is thickened, about 2 minutes.  Taste to see if it needs more salt or pepper.  Add a little more liquid if it gets too thick.