1. Finely chop the shallots and put them to heat in a small saucepan with 2 glasses of red Bordeaux.
2. Flavour with thyme, salt, mignonnette pepper and a pinch of grated nutmeg.
3. Reduce by three-quarters over high heat, then reduce flame intensity and whisk in 60 g of butter to reduce hazelnuts by hazelnut.
4. Cook 15 min over very low heat without boiling and whisk all the time.
5. 5 min before serving, chop the beef marrow and stir in the sauce, stirring with a spoon.
6. Continue to keep an eye on your Bordeaux wine so that it doesn't boil.
7. Just before serving, taste, adjust the seasoning and sprinkle with a pinch of parsley.
This sauce goes particularly well with grilled or roasted red meats and is also used in various preparations.