Bordelaise Sauce
from http://marinatemebaby.com/

Bordelaise sauce is a classic French sauce named after the Bordeaux region of France, which is famous for its wine. The sauce is made with dry red wine, bone marrow, butter, shallots and sauce demi-glace. Sauce marchand de vins ("wine-merchant's sauce") is a similar designation. Traditionally, bordelaise sauce is served with grilled beef or steak, though it can also be served with other meats that pair well with red wine demi-glace based sauces.

To save time, you can prepare the bordelaise sauce a day or two in advance and refrigerate it until ready to serve.

2 1/2 cups dry red wine (preferably not Merlot or Pinot Noir)
4 tablespoons shallots (finely chopped)
1/2 teaspoon ground black pepper (more if needed)
2 sprigs fresh thyme
1 bay leafe
1 1/2 oz Demi-Glace Gold (dissolved in 1 cup warm water)
2 teaspoons lemon juice
1/2 cup beef marrow (diced, soaked for 2-3 min in hot water and drained or 1/2 cup (1 stick) chilled unsalted butter, diced)
Kosher salt
Pinch ground allspice
Pinch cayenne pepper

In a saucepan, combine wine, shallots, pepper, thyme, and bay leave. Bring the mixture to a boil and cook until the liquid is reduced by about 2/3 cup.

Whisk in the Demi-Glace and simmer the sauce for 15 minutes.

Strain the sauce through a fine mesh sieve into a clean saucepan. Place the pan over low heat, then whisk in your lemon juice and beef marrow (or butter if your substituting), and continue to whisk until the marrow melts into the sauce. Season the sauce to taste with any additional pepper, allspice and cayenne.