Rescuing a tough brisket roast

Brisket is not a roasting cut; you didn't miss your train, it never left the station. Brisket is a very tough cut because of the presence of collagen, which breaks down at 72°C, and needs the presence of liquid, so roasting is not a good technique for this cut. If you'd taken it out when the alarm sounded it would be even tougher.

You can't roast things in a crock-pot, you have to have food mostly submerged in liquid for it to heat. There's no real target temperature for brisket in a crock pot in the sense of 'when it hits this temperature it's done' because you need to get it to at least 72°C and keep it there for hours so the collagen breaks down. If you use a temperature probe 72°C is when the cooking clock starts.

As for what to do now I would put all the brisket in an oven dish with a lid, put in some stock to about 2/3 of the way up and then braise it for at least 3 hours at about 145°C. Braise it until it starts to get tender, then braise it for a bit longer.

Brisket isn't the greatest cut for roasting, but it is possible. If you haven't fully sliced it, you can submerge it 2/3 in stock and cook it at 140 °C for about three hours or until tender. Then retrieve it and coat it in your favorite BBQ sauce and a rub, then roast at 180 °C for about 30 minutes, or until it looks shiny and somewhat caramelized.

If you have fully sliced it, I'd suggest cubing the meat and placing it into a stew. Allow the stew to simmer for about four hours and you'll have a very tender treat.

I haven't had hard brisket (which I usually boil), but I've had hard beef roast, and I added a little water to a frying pan (with whatever bits were in the original pan) and broke down the roast gradually into small bits as it softened, adding more water as needed. The meat got moister and was fantastic, and the liquid reduced and was flavorful for dipping into. I've since done this with leftover roast beef, too.