Trim the meat, making sure you cut out the nerves. You can also ask your butcher to do so.
Then cut (au couteau) the meat into small cubes with a knife, not a grinder.
Chop the shallots, capers, tarragon, and slice the cornichons.
In a salad bowl, mix the mustard, Tabasco, Worcestershire sauce, ketchup, olive oil, salt, and pepper. It’s really up to you to balance the sauce how you like it. You can put more or less Tabasco, mustard, etc.
Trust your own taste.
Add the meat to the salad bowl and mix gently before adding the shallots, capers, tarragon, and capers.
Break the eggs and separate the yolks into a separate container
Toast the bread on the stove or with your toaster.
Season your Boston lettuce with lemon, olive oil, salt, and pepper to your taste.
To serve, place a generous portion of Tartare, sprinkle some crispy fried onions over the top, and add the egg yolk to the center of the Tartare.
In a separate bowl, serve the salad and eat the Tartare with the toasted bread.