Peel and finely chop the onion and garlic, then finely grate the lemon zest. Clean and slice the mushrooms. Pick and finely chop the parsley. Place the beef between 2 sheets of clingfilm. Bash with a rolling pin until ½ cm thick, then cut into finger-width slices.
Mix the paprika, lemon zest, and a pinch of sea salt and black pepper together, and use to dust the beef. In a large frying pan over a medium-low heat, fry the onion and garlic in a little oil until softened. Turn up the heat and add the mushrooms and butter, sautéing until the mushrooms are golden brown, then tip onto a plate.
Add a little oil to the pan and fry the beef for 2 minutes, turning, until browned but still pink inside. Stir in the mushroom-onion mixture, add the brandy and reduce for 1 minute or until almost disappeared. Remove from the heat and stir in the cream, gherkins and parsley.
Serve with crusty bread.