Steakhouse-Style Beef Tenderloin Sandos

Toss potatoes on a baking sheet with a large drizzle of oil, half the garlic powder (you'll use the rest later), salt, and pepper. Roast on top rack until browned and tender, 20-25 minutes.

Meanwhile, in a small microwave-safe bowl, combine shallot, vinegar, ½ tsp sugar, and ½ tsp salt (1 tsp sugar and 1 tsp salt for 4 servings). Cover tightly with plastic wrap and microwave until shallot is softened, 30-60 seconds. 

Stir, then refrigerate until ready to use in Step 5. 

Pat beef* dry with paper towels; season all over with remaining garlic powder, a big pinch of salt, and pepper.

Heat a large drizzle of oil in a large pan over medium-high heat. Add beef and cook to desired doneness, 4-7 minutes per side. 

In the last minute of cooking, add half the garlic herb butter (you'll use the rest later). Baste the beef by gently tilting the pan and spooning melted butter over beef.

Turn off heat; transfer beef to a cutting board to rest. 

While beef cooks, in a large bowl, toss arugula with 1 TBSP olive oil, 1 tsp shallot pickling liquid, a pinch of salt, and pepper (2 TBSP olive oil and 2 tsp shallot pickling liquid for 4 servings). 

Spread remaining garlic herb butter onto cut sides of bottom halves of baguettes. Place gouda on cut sides of top halves. Place baguette halves, cut sides up, on a second baking sheet; bake on middle rack until cheese melts and bread is toasted, 2-4 minutes. 

In a second small bowl, whisk mayonnaise with as much truffle seasoning as you like.