Tenderloin steak sandwich with sticky caramelized onion recipe


The solution is a beautifully cooked piece of mustard crusted beef tenderloin that’s been properly rested and thinly sliced. It’s melt in your mouth meat, perfect for working into a killer sandwich with caramelized onions, sautéed buttered mushrooms, and peppery arugula all on a toasty baguette.

  • Yield: 4 Servings


Tenderloin steak sandwich with sticky caramelized onions, sauteed mushrooms, and arugula
  • 1 Tbsp Dijon mustard
  • 1 Tbsp whole grain mustard one
  • 8–10 oz portion beef tenderloin
  • 2 Tbsp coarse sea salt
  • 2 Tbsp coarsely cracked black pepper
  • 3 Tbsp olive oil
  • 4 Tbsp butter (divided)
  • 2 onions, thinly sliced
  • 4 cups mixed mushrooms (cremini, portobello, and button are ideal)
  • 1 sprig thyme
  • black pepper
  • 1 French baguette
  • 1 cup baby arugula, washed
Crispy buttermilk onion rings
  • 3 cups buttermilk
  • 1 Tbsp garlic powder
  • 1 sprig thyme, leaves only
  • 1 sprig marjoram, leaves only
  • 1 Tbsp salt
  • 1 tsp pepper
  • 2 Vidalia onions, cut into ½-inch thick rings
  • 2¼ cups flour (divided)
  • 4 cups vegetable oil for frying
Double-Onion Dip
  • 1 cup roughly chopped Vidalia onions (leftover pieces from the onion ring recipe can be used)
  • 1 Tbsp olive oil
  • ¾ cup sour cream
  • ¾ cup mayonnaise
  • 2–3 dashes hot sauce
  • 2 green onions, chopped
  • salt
How to Make It
    Tenderloin steak sandwich with sticky caramelized onions, sauteed mushrooms, and arugula
  1. Preheat oven to 400°F.
  2. To prepare steak, combine Dijon and whole grain mustards in a small bowl. Smear beef tenderloin with mustard mixture and then coat with sea salt and pepper on all sides to form a crust. Heat olive oil in a cast iron or heavy ovenproof skillet over high heat. When oil begins to smoke, sear all sides of beef until crust is deep golden brown. Place skillet in oven to finish cooking, about 10 minutes for medium-rare. Remove from heat and let rest at least 15 minutes.
  3. To prepare onions, heat 2 Tbsp butter and 2 Tbsp olive oil in a medium skillet over medium heat. Sauté onions until softened and lightly coloured, about 5 to 7 minutes. Season with salt and pepper and set aside. To prepare mushrooms, heat remaining 2 Tbsp butter and 2 Tbsp olive oil in a medium skillet over high heat. Sauté mushrooms and thyme until well coloured, about 8 to 10 minutes. Season with salt and pepper.
  4. To assemble sandwiches, combine dijon and whole grain mustards. Carve steak into thin slices, reserving any juices. Split baguette into 4 portions. Toast each lightly and spread thinly with mustard mixture. Fill each sandwich with steak, sautéed onions, and mushrooms. Top with arugula and spoon over any steak juices. Serve with hot onion rings.
  5. Crispy Buttermilk Onion Rings
  6. Combine buttermilk, garlic powder, thyme leaves, marjoram leaves, and salt and pepper in a large bowl. Soak onion slices, making sure they are covered in buttermilk mixture, in the refrigerator for at least 60 minutes; Overnight is best.
  7. Preheat oven to 250°F.
  8. Drain onions, reserving buttermilk marinade. Place 2 cups of the flour in a medium mixing bowl; slowly whisk in enough reserved marinade (about 2 cups) to form a loose paste the consistency of pancake batter.
  9. Fill a small deep saucepan about 1½ to 2 inches deep with vegetable oil, making sure oil does not reach more than halfway up saucepan. Heat oil to 340–350°F. Lightly flour onion rings with remaining ¼ cup flour. Dip into batter and drop, 1 or 2 at a time, into oil. Fry until deep golden brown and drain on a paper towel–lined plate. Season onion rings with salt while still warm. Keep onion rings warm.
  10. Double-Onion Dip
  11. Preheat oven to 350°F.
  12. Place vidalia onions in a piece of aluminum foil and drizzle olive oil over them. Wrap in a loose package and bake until tender and golden, about 15 to 20 minutes.
  13. Unwrap and when cool enough to handle, chop into a rough mash. Combine sour cream, mayonnaise, and hot sauce in a medium bowl. Add chopped onion and green onions. Fold to combine and season with salt. Cover with plastic wrap and keep refrigerated.

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