Step 1 Parmesan baskets: Line two baking trays with baking parchment. Sprinkle the Parmesan evenly over the baking parchment to form 4 circles(approx. 15 cm in diameter).Bake these in a preheated oven at 200°C(top and bottom heat) for approx.8-10 min. Take the trays out, leave them to stand briefly and then with the aid of a palette or a pancake turner/fish slice lay the Parmesan rounds over small bowls and lightly press them down. Leave them to set hard.
Step 2 Sauce tartare: Chop the egg, the small onion, the parsley and the pickled gherkins up fine. Stir them with the mayonnaise, lemon juice and mustard until smooth. Season the sauce with salt and pepper to taste. Place it in the refrigerator.
Step 3 Rinse the leaf salad, dab it dry and fill the finished Parmesan baskets with it. Arrange two roast beef slices to form rosettes in each of them. Halve the cherry tomatoes and cut the red onions into fine wedges. Deal both of these out evenly between the Parmesan baskets. Finally, garnish them with sauce tartare and serve.