Hi C.,
When I have a large group to feed and want something easy to prepare so I can actually enjoy the party...I make beef briskets. It is a two day process...which I know sounds like a lot of work...but it couldn't be easier!
I suggest you buy/borrow one or two electric roasters...much easier and less costly than using your oven...plus you won't heat the house up. (And they travel easy in case you're having the party at a hall, etc.)
Day 1
Trim excess fat from the briskets
Put the briskets in a roaster (you can fit a few in each...they shrink quite a bit during cooking).
Sprinkle each with salt, pepper, celery salt and garlic salt/powder. (you can add any other seasonings you are fond of) Sprinkle each with beefy french onion soup mix, one envelope per brisket.
Add enough water to almost cover the briskets.
Cover and cook at 325 for about 4 hours. (You may need to add water as you go. This will be your au jus when you serve the brisket.)
Remove briskets, let cool and then slice (against the grain, about 3/4" thick slices) and place back into the liquid. Cover and put in fridge over nite.
Day 2
Scoop and remove any excess fat from the top. Put roaster back on 325 and let simmer for another 4-5 hours.
Add water if needed, and I usually add a couple more packets of the beefy onion soup mix.
You're better off to cook it too long instead of not long enough. The longer it stays in the roaster...the more delicious and tender it gets. It can stay in there all day as long as it is kept hot.
It really is easy and leaves you free to deal with your side dishes and enjoy your guests.
I buy 3/4" sliced bread (the brand I've found is called "Big Texas") and people love to make an open face "hot beef sandwich" by putting the brisket on a slice of bread and drizzling it with the au jus. (I'm getting hungry just thinking about it!)
Everyone I have made this for has been floored at how good it is. Honestly...we are not big beef eaters in my family...but my brother made these briskets for a family gathering and it has become a staple ever since.
I get my briskets at Costco...good price...great selection. If you have a meat market, you could check with them, too. I think it is usually about $3.99/pound at Costco.
An easy side is lots of mashed potatoes...they keep well in a roaster or crock pot also. (Make them a little more moist than you usually would).
Good luck!
L.