Season steak with salt and pepper, and firmly press seasonings into steak. In a large heavy skillet over medium heat, combine clarified butter, sage, thyme and rosemary. Cook until herbs begin to brown, then remove herbs.
Increase heat to medium-high. Sear steak for 10 to 15 minutes on each side. Carefully pour brandy over steak. Stand back, and ignite the brandy (flames can be quite intense). When flames die, remove steak from pan; keep warm.
Stir demi glace into pan, and deglaze the pan, scraping up any bits stuck to the bottom. Simmer until liquid is reduced by half. Stir in heavy cream, and any juices that have accumulated under the steak. Add roux to sauce to thicken to a smooth, rich consistency. Taste sauce and add more peppercorns or salt if desired.