For the crumble topping:
Heat the olive oil in a skillet on medium heat and add the leeks and onions. Cook, stirring occasionally, for 10 minutes or until the vegetables are softened. Add the drained spinach and cook until heated through. Season lightly with salt and pepper.
Meanwhile mix the salmon pieces with the crème fraîche, dill, mustard, lemon juice and salt and pepper.
Place the butter, flour, bread crumbs and parmesan cheese in a bowl and crumble together with a pastry blender. The mixture should resemble coarse bread crumbs.
In a greased 13X9 inch Pyrex baking pan or equivalent, spread the spinach into an even layer. Top with the salmon and then sprinkle with the crumble.
Bake at 350°F for 40 minutes. Serve hot. Goes well with wild rice.
Makes 6 servings.
If you want to make this recipe ahead of time, prepare the salmon and fish layers, then cover and refrigerate. Mix the crumble and refrigerate separately. Sprinkle the casserole with the crumble just before baking.