Place a large non-stick pan over medium heat, then add a light drizzle of oil. Add the spinach and use your wooden spoon to press down, then begin stirring the spinach. Once the spinach has wilted, use tongs to remove it and place it on 2-3 linings of kitchen roll/paper towels. Place more on top and press down to squeeze out the excess moisture.
Use kitchen roll/paper towels to pat the salmon dry, then season both sides of the fillets with a good pinch of salt and black pepper.
Turn the heat to medium-high and add a drizzle of oil. Once hot, add the salmon presentation side down and fry for 3 minutes, or until golden and crisp on the bottom. Carefully flip and fry them for 2 minutes, then add the butter and baste them for 1 more minute, or until they're just about cooked through and golden on both sides. Remove the salmon and place on a plate to one side, then lower the heat to medium.
Add the shallots to the leftover butter and fry until soft and golden, then add the garlic and fry for 30 seconds or so longer (be careful it doesn't burn). Pour in the wine, increase the heat to a rapid simmer and cook for 3-4 minutes, or until it almost completely evaporates and the pungent smell of alcohol vanishes.
Lower the heat back down to medium and pour in the stock and cream. Stir in the parmesan, salt, white pepper and nutmeg until blended, then simmer for a few minutes until the sauce thickens. Stir in the resting juices from the salmon, then check for seasoning and adjust if needed. You can now stir in the spinach (the sauce might be quite thick, but the spinach will thin it out a little more).
I like to serve with a light zesting of lemon on top, then a lemon wedge per person to squeeze over at the end. You can also slice 2 thin rings from the lemon and halve them, to make 4 semi-circles to garnish the salmon.