The tangy, bitter flavour of capers adds piquancy to many sauces and condiments, such as tartare sauce, and they are a good match for fish. They can be used as a garnish for meat and vegetable ...
Stir in remaining vinegar, cornichons, capers, chile flakes, parsley, thyme and sugar to make a coarse sauce. Season with salt and pepper. Spoon sauce over steak and let rest together 5 minutes.
Then the leftover marinade in the bowl (plus some water and honey) becomes a punchy pan sauce, with butter added for a velvety texture and whole capers for pops of tang. Heat remaining 2 Tbsp.