Brisket is a cut of meat that is shied away from mostly because people know it's tough. If you know this up front all you have to do is prepare to deal with it!
The
beef brisket comes from the breast section right under the first five or
six ribs. It is a dense meat (very little or no marbled fat) and cooking
it to be tender is a time consuming yet easy chore. It's all in
the preparation and most importantly in the cooking. This is a method I use for your regular 6 - 9 lb. brisket untrimmed. I won't buy the trimmed brisket unless it will be put in a soup or something.
You can experiment with the seasonings for this.
Marinade:
1 cup whole milk or buttermilk
1 tbs. Garlic powder
1/3 cup lemon juice
Mix together well....
Marinade brisket in it's original cry-o-pack if that's what it came in. With the fat side up slit the plastic about 6 inches so you can pour the marinade in. Work it around best you can and refrigerate overnight.
I'll allow about 1/2 hour per pound to cook the brisket at 225 - 250º F. This is an estimate, some briskets are tougher than others. When I purchase a whole brisket I look for the smallest one in the case. I figure the smaller the brisket the smaller the cow the more tender the meat.
When ready to cook take the brisket out of the plastic and save the marinade. Rub the brisket down with any seasonings you like trying not to use any that contain too much salt. Lightly oil a roaster or pan with at least 2" sides, place the brisket in fat side up. Pour in the marinade and about a cup of water. Lay 6 - 8 slices of bacon on top.
To start cook uncovered at 400F to get it brown on both sides (you flip it). You can also brown it on top the stove if you have a pot big enough. Lower the heat to 250F.
Check it every 30 minutes or so to be sure there is still water in the pan and add as needed. After the initial few hours cover the pan. Heavy duty aluminum foil will work if you don't have a cover.
An hour or so before it's done slice some mushrooms, onions and bell peppers (cubed - 1" X 1"). Put them in with brisket adding enough water or beef stock just to cover the vegetables. Add about a tsp. each of creole seasoning, black pepper, and, 1 each tbs. Worcestershire and soy sauce. Cover again and let it cook.
Now the tricky part "when do I know it's done?". Generally you can take some tongs and grab one side of the brisket and bend it. If the meat looks like it wants to separate it's done. When I say done I mean tender enough, not cooked to a certain temperature which of course you should check also.
I'll sometimes just cook it till it all falls apart to use for sandwiches but you'll have to deal with slicing stringy meat.
You can cook the brisket in the oven or the pit if it's big enough to keep the pan away from the fire. You can also start it in the oven and finish it in the pit for a smoked flavor. You have several choices on the heat source.
When
all is done you need to discard the fat. If it's been cooked enough you
can take a knife and scrape the fat (knife perpendicular to the grain)
right off the meat with the knife's edge as shown in the picture 
When
slicing the brisket look for the grain and slice it first (with the
grain) in the widths you want as shown here. I'm going to slice these
opposite of the first slices.
Then,
cut it against the grain. I like to use an electric knife for this. This
is a dense and naturally tough meat, so the thinner the slices the
better the meat. Most briskets will have two distinct pieces of meat separated by fat and each piece of meats' grain is running opposite ways. To properly cut it you should separate these two pieces, remove any fat, and, cut them individually.
This brisket is is only half (the smaller portion) of the large one shown at the beginning of this recipe.
When
all the meat is sliced take the meat and put it in a casserole dish,
then, pour the gravy and vegetables over the brisket. Let it rest for
about 15 minutes. Taste it and sprinkle seasoning as you like. Makes
great sandwiches!