French Chateaubriand

500 g beef tenderloin
2 tbsp butter
2 tbsp olive oil
SIDS SALT & PEPPER to taste
1 shallot, finely chopped
½ cup dry red wine
½ cup demi-glace
1 tbsp butter, softened
1 tbsp fresh ​tarragon or 2 tsp dried​

Preheat the oven to 190°C.
Melt the butter and olive oil together in a large frypan set over medium-high heat until the mixture turns a bit cloudy and bubbly.
Season the beef with SIDS SALT & PEPPER to taste then place the meat in the pan and do not move it at all for at least 3 minutes. Using tongs, carefully turn the tenderloin on its side and brown it for 3 minutes. Repeat the same browning process on all exposed surfaces of the meat.
Place the tenderloin on a rack in a roasting pan in the oven. Roast for 15 minutes for medium-rare, 20 minutes for medium and 23 minutes for medium-well.
Transfer the chateaubriand to a warmed serving platter, lightly tent it with a single layer of foil to rest, untouched, for 15 minutes.
While the tenderloin is resting, make the wine sauce. Sauté the chopped shallots in the leftover pan juices in the pan until softened and translucent. Pour the wine into the pan and bring the sauce to a boil, scraping up all the browned bits on the bottom of the pan. Continue boiling the sauce until it reduces by half. Add the demi-glace to the sauce and continue boiling the mixture until it becomes slightly thickened.
Remove the sauce from the heat and stir in the tarragon and softened butter.
Serve the chateaubriand, sliced on the diagonal, with the wine sauce and chateau potatoes or truffle fries.
Tips: If you do not have demi-glace, though this will not be as good as one, you can reduce a can of top quality beef consommé by half and use as above.
Resting the Chateaubriand is paramount to creating the perfect slice. By cooking with time to rest the meat means juices are released (needed for the sauce) and the fibres in the meat relax thus making the eventual eating extremely tender.
History: Demi-glace ("half glaze") is a rich brown sauce in French cuisine used by itself or as a base for other sauces. The term comes from the French word glace, which, used in reference to a sauce, means "icing" or "glaze". It is traditionally made by combining one part Espagnole sauce and one part brown stock. The sauce is then reduced by half, strained of any left over impurities and finished with a sherry wine. Common variants of demi-glace use a 1:1 mixture of beef or chicken stock to sauce espagnole; these are referred to as "beef demi-glace" (demi-glace au boeuf) or "chicken demi-glace" (demi-glace au poulet). The term "demi-glace" by itself implies that it is made with the traditional veal stock.