Add the butter to a large 2-gallon pot over medium heat. Once it’s melted add in the onions, celery, and carrots, and sauté for 25 to 30 minutes while frequently stirring with a spoon or until well caramelized.
Next, stir in the tomato paste and cook for 8 to 10 minutes to deepen the flavor and becomes a rust-like color. This is process is known as pince.
Pour in the veal stock.
On a 1 x 1 square foot piece of cheesecloth, place to the center the thyme, parsley, peppercorns, and garlic. Fold up the corners and securely tie a double knot around it using butcher’s twine to ensure nothing is coming out. As a note, if you plan on using a chinois to drain everything, you can just place everything in the cheesecloth into the pot.
Simmer over low to medium heat for 2 hours and be sure to come back every 30 minutes to skim and discard any impurities or fat that collects at the top.
With about 30 minutes left in the simmering process melt the 2 sticks of butter in a large sauté pan over low to medium heat.
Once melted whisk in the flour until combined. Whisk frequently for the next 20 to 25 minutes to create a dark roux.
At this time slowly pour the roux in the stock pot of stock and veggies while continually whisking until it is incorporated. The stock will immediately thicken.
Cook for a further 20 to 25 minutes.
Strain the stock completely through a chinois, fine mesh strainer, or cheesecloth. Use, or store in the fridge or freezer.
Notes
Make-Ahead: Making this sauce 1 or 2 days before serving will give the flavors more time to meld and intensify. If you need to keep it warm before serving, pour the sauce into a saucepan over low heat, stirring occasionally, until it’s time to eat.How to Store: Transfer the leftover espagnole to an airtight container once it has cooled completely. It will keep in the fridge for up to 5 days or in the freezer for up to 3 months. If freezing, leave a little room at the top of the container for expansion.How to Reheat: Reheat the sauce in a saucepan over low to medium heat, stirring occasionally. If it becomes too thick, add a splash of water or stock to loosen the consistency.Be patient when sautéing the vegetables. Giving them time to caramelize will build the savory base of the sauce. The more golden the vegetables are (without burning), the more decadent your sauce will be.When making the brown roux, keep a close eye on the heat and whisk it frequently to prevent burning. It takes time to achieve the desired deep golden brown color, but it’s worth it since it lends significant richness and body to the sauce.To make a bouquet garni, place the herbs, peppercorns, and garlic in the center of a square of cheesecloth. Fold the corners and tie it securely with butcher’s twine.You can also skip wrapping the bouquet garni in cheesecloth if you plan on straining the sauce through a chinois or cheesecloth.Stir the sauce often during the last 20 to 25 minutes of cooking to prevent it from scorching (burning at the bottom of the pot).Skim the impurities and fat at the top of the sauce every 30 minutes to ensure a velvety consistency.If the espagnole sauce is too thick, stir in a splash of stock or water.If it’s too thin, simmer it longer until it reduces and reaches your desired consistency