Step 1

Slice all onions thinly and set it aside.

Step 2

Preheat a large cooking pan oven medium heat. Melt butter and add onions, salt, and sugar. Mix very well until onions are evenly seasoned. Let onions cook until all softened, mixing from time to time.

Step 3

Pour in white wine and let it cook for 2-3 minutes.

Step 4

Mix beef stock, tomato sauce, white wine vinegar, pressed garlic, thyme, salt, and paprika in a mixing bowl and pour it into the pan with onions.

Step 5

Stir carefully and let it simmer for 5-7 minutes. Take off heat.

Step 6

Preheat the oven to 300°.

Step 7

Use two long sheets of aluminum foil to place them in the bottom of a roasting pan side by side but overlapping. Make sure the roasting pan fits the brisket nicely, not too bit and not too small.

Step 8

Spread 1/3 of the sauce and onion in the bottom of the pan, on the foil. Place brisket on top of the onions, fat cap up.

Step 9

Spread remaining French Onion sauce over the brisket and close the foil around the brisket to create a pocket. If the brisket is large, you may need to cover with another sheet of foil on top and tuck it under.

Step 10

Place in the oven and cook for about 6 hours.

Step 11

Open the foil and cook for another 45-60 minutes uncovered.

Step 12

Take the roasting pan out of the oven and take the brisket out of the pan and onto a cutting board. Loosely tent with a sheet of foil and let the brisket rest for about 15 minutes before slicing.

Step 13

Use a sharp knife to slice across the grain when ready.

Step 14

Pour all onions and sauce out of the roasting pan and into a sauce pot.

Step 15

Mix cornstarch with some cold beef stock and stir it into the sauce.

Step 16

Bring the sauce to simmer over medium heat and cook it until thickened, stirring often.

Step 17

Take it off heat and spoon it over sliced brisket and potatoes when serving.