1 tablespoon browning sauce (such as Kitchen Bouquet®), or as desired
1 tablespoon vegetable oil
1 onion, sliced
6 cloves garlic, sliced
2 tablespoons water
Preheat oven to 275 degrees F (135 degrees C).
Discard any flavoring packet from corned beef. Brush brisket with browning sauce on both sides. Heat vegetable oil in a large skillet over medium-high heat and brown brisket on both sides in the hot oil, 5 to 8 minutes per side.
Place brisket on a rack set in a roasting pan. Scatter onion and garlic slices over brisket and add water to roasting pan. Cover pan tightly with aluminum foil.
Roast in the preheated oven until meat is tender, about 6 hours.