Take the steaks out 30 minutes before cooking and season them with salt.
Heat the oven to 220°C.
Boil the potatoes in well-salted water for 15 to 20 minutes, until fork-tender.
Drain and let them steam dry for a few minutes.
Transfer the potatoes to a sheet pan, smash them gently, drizzle with olive oil, and season with salt and pepper.
Roast for 25 to 30 minutes, turning once, until crisp and deeply golden.
Pat the steaks dry, brush one side lightly with Dijon, and press that side into the crushed peppercorns.
Heat a heavy skillet over medium-high heat and add the olive oil.
Sear the steaks peppercorn-side down first for 3 to 4 minutes per side, until browned and cooked to your liking.
Transfer to a plate and rest loosely covered.
Lower the heat to medium and add the butter, thyme, garlic, and shallot.
Cook for 1 minute, until fragrant.
Add the brandy and scrape up the browned bits.
Pour in the stock and simmer until slightly reduced.
Stir in the crème fraîche and cook gently until the sauce is smooth and lightly thickened.
Spoon the sauce over the steaks and serve with the potatoes.