1 cup sour cream
2 tablespoons prepared horseradish
1 teaspoon Dijon mustard
1 center-cut beef tenderloin, 2 to 2-1/2 pounds
Extra-virgin olive oil
1 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
1 large French baguette, sliced in half lengthwise
1 bunch arugula, washed and dried
1 cup grated Fontina cheese
1. In a small bowl, mix together the sour cream, horseradish, and mustard. Set aside.
2. Lightly brush or spray the tenderloin with the olive oil and season with salt and pepper. Allow the tenderloin to stand at room temperature for 20 to 30 minutes before grilling. Sear over Direct High heat until well marked, 8 to 10 minutes. Continue grilling over Indirect Medium heat until the internal temperature reaches 140 F for medium rare, about 20 minutes. Remove from the grill, and let rest for 3 to 5 minutes. The internal temperature will rise 5 F to 10 F during this time. Cut into 1/8-inch slices.
3. Lightly brush the cut side of the baguette with olive oil and grill, cut side down, over Direct Medium heat until lightly toasted, about 30 seconds.
4. Spread the baguette with the sour cream mixture, layer with arugula and sliced tenderloin, then top with the grated cheese. Cut crosswise into individual sandwiches.