Preheat oven to 300 degrees.
Trim your brisket of all visible fat, leaving a 1/2 inch layer of fat on the flat side, and little to no visible outer fat on the point (You can save your fat trimmings to make tallow later on!).
Coat your brisket thoroughly with the salt and pepper. You want to be able to see it all over!
Lay the onions on the bottom of your large roasting pan. The onions will act as a rack, and also infuse flavor into the brisket.
Pour the bone broth over the onions.
Lay the brisket on top of the onions, making sure it is not touching the bottom of the pan. Pro tip: if you think you need more onions, add a few more!
Cover the pan tightly in aluminum foil.
Bake the brisket for up to 4 hours in the oven. Every 20-30 minutes, remove from the oven and baste the brisket with the bone broth. This will ensure that the outer layer of the brisket doesn't dry out.
In the last hour of cooking, remove the foil so the brisket can get some color to it and become golden brown.
Once the brisket reaches 205 degrees, remove from the oven, and allow it to rest with the foil vented for 30-minutes to 1 hour.
Slice and serve along with the onions!