If you could cross baby spinach with lemon, you’d get something like sorrel. It brightens salads, sauces and omelets, but best of all makes a marvel of a soup. And nothing captures the flavor and simple pleasures of the French countryside like this dish: French Sorrel Soup. Remarkably fast and easy to make, this elegant, tangy soup goes from zero to the table in less than 15 minutes. No potatoes, no aromatics, no cream. An egg yolk swirled in at the end adds a bit of richness, and some toasted bread served in the bowl gives it depth. The hardest part might be finding the main ingredient. Popular throughout Europe, sorrel is rarely seen…