Open steak sandwiches with dark fried onions and béarnaise mayonnaise

Step by Step

Step 1

To make the mayonnaise, mix the egg yolk and mustard in a bowl. Season. Using electric beaters, add the oil a little at a time, beating continually, only adding the next amount of oil when the previous one has been incorporated and the mixture has thickened. Do this until all the oil has been used. Add the white wine vinegar, shallot and herbs. Taste for seasoning and set aside.

Step 2

Take the steaks out of the fridge 20 minutes before cooking and brush with oil on both sides. Meanwhile, add the rest of the oil to a large frying pan and fry the onions, first on a medium heat until soft, then on a higher one to crisp and darken them. It will take 12-15 minutes. Lift them out of the fat onto a double layer of kitchen paper. Sprinkle with a little salt. Transfer the onions to a bowl.

Step 3

Re-heat the pan, plus another one so you have enough room for all 4 steaks. Once the pans are really hot, season the steaks and add them. Cook over a high heat, turning every 30 seconds or so, until they have a good brown crust. Each one will take about 3 minutes in total for rare (longer if using thick steaks). Remove to a plate, cover with foil and leave to rest for 5 minutes.

Step 4

Spread some of the mayonnaise on each piece of bread. Remove the coarser stalks from the watercress and put sprigs on top of the bread. Slice the steaks, cutting on the diagonal. Divide the meat between the 6 slices of bread. Add some onions, but not so many that you can no longer see the pink meat. Spoon some of the mayonnaise on top, add a sprig of parsley and serve immediately.