Slice the fennel and leek. Place alternating layers of fennel and leek into a baking tray greased with butter. Sprinkle each layer with salt and drizzle with lemon to keep the fennel from turning brown.
Heat a tablespoon of butter in a pan, add a tablespoon of flour and mix continuously to make a roux. Once the roux is cooked out, gradually add the wine, mixing continuously as the alcohol evaporates. Once again gradually, add the milk to achieve a creamy consistency. Season with salt and pepper and add a pinch of nutmeg.
Pour this béchamel over the fennel and leek and sprinkle parmesan over the top. Place the baking tray in a pre-heated oven at 170°C for 15-20 minutes until a golden crust forms on the top.
Toss the almond slices in a dry hot pan and turn them out as soon as they take on a golden colour.
Wipe the pan and add a tablespoon of olive oil, turning the pan to coat the bottom with the hot oil. Place the salmon skin side down into the pan and hold it down to the pan for a moment. Fry the skin until golden brown.
Add a tablespoon of butter to the pan and, using the spoon, pour the butter over the salmon. Season with salt and pepper. Coat the salmon in the toasted almond slices and serve with the fennel gratin.