For the sauce:
Chef Caswell recommends using the inside of about a quarter loaf of airy white bread, such as Essential Baking Company's ciabatta. If you can't find verjus, which is the juice of under ripened grapes, substitute a squeeze of lemon juice.
For the salsa verde:
Place basil, parsley, mint, garlic and salt in the work bowl of a food processor. With the machine running, add the olive oil in a slow, steady stream. Add chunks of bread and continue to process until bread is gravel-sized. Add verjus or a couple of squeezes of lemon, tasting for a balance of acidity and sweetness. Set aside at room temperature. (If made the day before, refrigerate and bring to room temperature before serving.)
For the vegetables:
Heat a large, heavy bottomed saut pan over medium-high heat. Add the olive oil and one tablespoon of the butter, then garlic and shallots. When the garlic and shallots become fragrant, add zucchini, carrots, radishes, turnips, and sugar snap peas. Saut for 2 to 3 minutes; the veggies' colors will brighten. Season with salt and pepper. Add spinach and kale and saut an additional minute or so, until the greens are wilted. Finally, add the blossoms and allow the heat of the vegetables to wilt the blossoms. Stir in the remaining tablespoon of butter and a splash of verjus. Taste again for seasoning.
Cook the salmon:
Meanwhile, season both sides of salmon fillets with salt and pepper. In a large non-stick saut pan, heat the olive oil until almost smoking over medium-high heat. Add the butter. As the butter is browning, add the salmon, skin side down. Using a spatula, press the salmon into the pan, and decrease heat to medium-low. Allow the skin to crisp for two to three minutes, then carefully flip the fish over in the saut pan. Turn the heat off and allow the fish to cook in the residual heat for another minute or so. (You may need to increase cooking time, depending on the thickness of your salmon.)
Distribute the cooked vegetables evenly on four dinner plates. Place one salmon fillet atop each pile of veggies. Spoon the salsa verde around the salmon and vegetables. Serve and enjoy. Wine Pairing: 2006 Pinot Gris from Seven Hills Winery. Hazelnut and green apple notes yield a bit of new French oak to this crisp wine.