Prepared in about 30 minutes, this sauce makes the wonders of brown sauce much more accessible. If made with mushroom stock, it is vegetarian.
Melt in a large wide saucepan over medium-high heat:
Add and cook, stirring, until well browned, about 10 minutes:
Reduce the heat to medium and add:
Cook, stirring, until the sugar and tomato paste, if using, are deeply browned (do not burn them). Carefully whisk in:
Bring to a boil and boil until reduced by half, 2 to 3 minutes. Whisk in:
Bring to a rolling boil over high heat and boil for 4 minutes. Strain through a fine-mesh sieve into a heatproof bowl and set aside. Melt in the same saucepan over medium heat:
Whisk in and cook, stirring, until the roux is walnut brown, 5 to 8 minutes:
Whisk in the strained stock along with:
Bring to a boil, whisking, and simmer briskly until it is the consistency of heavy cream, 15 to 20 minutes. Strain again, if desired, and if using as is, blend in: