How to Make It
Preheat the oven to 450°. Heat a 12-inch cast-iron skillet until very hot. Add the olive oil, shiitake mushroom caps, garlic and jalapeño slices and stir well. Season with salt. Transfer the skillet to the oven and roast the shiitake caps, stirring a few times, for about 20 minutes, or until richly browned and crisp.
In a large, nonstick skillet, heat the grapeseed oil. Season the salmon fillets with salt and white pepper and add them to the skillet, skin side down. Cook the salmon over high heat for 5 minutes, then reduce the heat to moderate and cook until the skin is browned and very crisp, about 12 minutes longer. Turn and cook the salmon for 2 minutes on the other side, until barely cooked through.
Transfer the salmon fillets to plates, skin side up. Gently lift the skin off the salmon and lean it against the fillet. Spoon the roasted shiitake caps on the salmon. Drizzle the plates with mushroom syrup and serve with the lemon wedges.