Grandma's Mushroom-Onion Brisket revised

Source: Grandma Lorraine
adapted by There's Always Thyme to Cook

brisket (flat cut)
1 envelope Lipton mushroom-onion soup mix
1/2 to 3/4 cup water
carrots, sliced thin
potatoes, cut in chunks
1 tablespoons flour (more or less)
mushrooms, quartered (optional)
sliced onions (optional)
*If you have porcini powder, you can sprinkle a little on the brisket, too, adds great flavor*

Preheat oven to 300 F.

Empty soup packet into a large cup and mix in the flour. Add water to the cup and stir to dissolve. Put the brisket in a large baking dish and add carrots, potatoes, mushrooms, onions and the soup mix. Cover with aluminum foil. Cook for a few hours, until the brisket is tender. Slice thin, against the grain and serve with the vegetables and gravy. It's even better the next day.