Season beef tenderloin generously with salt and pepper.

Heat a heavy-based skillet (preferably cast iron) over high heat. Add vegetable oil if not using cast iron.

Test pan readiness by touching the edge of one steak to the pan surface; it should sizzle briskly.

Immediately drop steaks in and sear one side for 2 minutes. Check for browning.

Flip steaks and sear the other side for 2-3 minutes.

Reduce heat to medium-high, cook for another 2 minutes, flip, and cook until a digital thermometer reads 120°F for rare, or 125°F for medium-rare (1-2 minutes).

Transfer steaks to a warm platter and let rest, covered loosely with foil, while making the sauce.

Return unwashed pan to medium heat. Add butter and let melt.

Add shallots and cook, stirring, until fragrant and just tender (1-2 minutes).

Add whiskey and stir with a wooden spoon, scraping up any browned bits stuck to the pan.

Add beef broth and Worcestershire sauce, raise heat to medium-high, and bring to a boil.

Whisk in mustard and then cream.

Continue to cook at a boil, stirring, until reduced to a saucy consistency (3-5 minutes).

Taste the sauce and season with salt, pepper, and lemon juice.

Serve steak with the sauce.