Take the steak out of the fridge an hour before cooking to allow it to come to room temperature. This ensures even cooking.
Peel russet potatoes and cut into 1/4-inch sticks. Soak in cold water for 30 minutes.
Chop the shallot.
Heat the butter over medium heat in a cast iron skillet and add shallots and sautè until browned.
Once the shallots have browned, add the Cognac and simmer for a few minutes over low heat to allow the alcohol to evaporate.
While simmering, use a knife or mortar and pestle to crush the green peppercorns, which will facilitate the next step. Add the crushed peppercorns to the pan. Pour in the beef broth and bring the mixture to a boil while allowing it to thicken.
Add the crème fraîche and salt to taste. Stir regularly as the sauce thickens. Drain and pat dry the potatoes with paper towels or a kitchen towel.
Pat the steaks dry with paper towels and season generously on both sides with coarse salt and freshly cracked black pepper.
In a separate large pot, heat several inches of vegetable or canola oil in a frying pan to 325 °F (160 °C) for the potatoes.
To cook the steak, heat 2 tablespoons of olive oil in a heavy cast iron skillet over high heat until very hot and shimmering.
Transfer steaks to the skillet and cook without moving for 3 to 5 minutes per side for medium-rare, flipping only once, until browned. The internal temperature should reach 135 °F (57 °C).
Cover the steaks with foil and let them rest for 5 to 10 minutes to allow the juices to redistribute.
While the meat is resting, fry the frites. Fry the potatoes in batches until limp but not browned about 5 minutes.
Remove and drain the excess oil on paper towels.
Increase oil temperature to 375 °F (190 °C). Fry potatoes in batches again until golden brown and crisp, about 2 minutes.
Drain again on paper towels and season with salt.
Slice the steak against the grain into 1/2-inch slices (about 1 cm). Serve with a generous portion of crispy french fries, or frites, and the sauce on the side.
A simple green salad completes this classic French bistro meal. Bon appétit!!