Beef steak with mustard sauce and potatoes

Ingredients:

• 500g beef flank steak or beef tenderloin, trimmed of excess fat
• 900 g peeled potatoes
• 3 tablespoons Dijon mustard
• 1 tbsp. l. olive oil
• Freshly ground black pepper and coarse salt
• 2 tbsp. l. chopped chives
• 1 tbsp chopped fresh tarragon
• 2 egg whites
• 1 teaspoon paprika
• Pinch cayenne pepper

Preparation:

1. Preheat oven to 230°C.
2. Prepare mustard sauce: Mix mustard and olive oil in a bowl. Rub 2 tablespoons of the mustard mixture over the beef steak, then season with black pepper and let sit. Add chives, tarragon, and 2 tablespoons of cold water to the mustard mixture.
3. Prepare potatoes: Cut the potatoes into strips and pat dry. In a large bowl, whisk together the egg whites, paprika, cayenne pepper, and 1/4 teaspoon salt. Add the potatoes and toss. Grease a baking sheet with vegetable oil. Drain any excess liquid from the potatoes and arrange them in an even layer on the baking sheet. Bake the potatoes until golden brown, 25 minutes.
4. Meanwhile, prepare the steak: Sprinkle a cast-iron skillet with 1/4 teaspoon coarse salt and heat until very hot. Add the steak and place a weight on top. Cook over high heat until crispy, about 3 minutes per side.
   
   Turn off the heat and let the steak cook in the pan for another 5-8 minutes. This will give you a medium-rare steak. Slice the steak thinly across the grain and serve with potatoes and mustard sauce.