I love cooking with summer leeks. They have less of the stiff green top and more of the tender white bottoms than their winter cousins. Their flavours are more subtle than other members of the onion family and they do not have an adverse effect on your breath. This soup is very simple and quick to make and can be made vegetarian by omitting the fish garnish. Or you can substitute char, sea trout, or even a white-fleshed fish like halibut or sturgeon. The possibilities are endless. The “caviar” or salmon roe is found or attainable at most good fish markets.
Sauté onion, leek and garlic in butter for 3 minutes. Do not allow any colour to form. Add thyme sprigs and white wine and reduce until wine evaporates. Add potatoes and stock and bring to a boil. Cook until potatoes are tender, add watercress and bring just to a simmer. Add cream at this point, if desired. Purée in a blender while still warm, season with salt and pepper, and serve immediately.
Scrape scales from the salmon skin with a knife or fish-scaling tool. Cut fillet into 6 equal-sized pieces. Pinching each piece between your fingers, make two small slices in the salmon skin, no more than 1⁄8-in (3-mm) deep. This will prevent fish from curling in the pan. Heat oil in a non-stick or cast iron frying pan. Add fish, skin side down, and cook for 4 minutes, until skin is crispy and slightly browned. Remove pan from heat and flip fish, allowing the residual heat in the pan to finish the cooking.
Ladle 6 to 8 oz (170 to 225 mL) of broth into a soup plate and place seared salmon in the centre of the bowl, crispy side up. Spoon a small amount of crème fraîche and a teaspoon of caviar on the skin, and garnish with sliced chives or a sprig of fresh watercress.