Three days prior to serving, place salmon on a baking sheet. In a small bowl, zest oranges and lemons, add salt and sugar, and mix. Spread mixture evenly over fish. Cover with plastic wrap and place another baking sheet on top of salmon. Weight down top sheet with several large cans or a heavy pot. Refrigerate for 3 days, flipping fish halfway through.
After 3 days, make baguette toasts. Preheat oven to 350°F. Slice baguette into ¼-inch rounds and place in a single layer on a baking sheet. Bake until golden, about 8 minutes. Repeat batches until all bread has been toasted. Cool and set aside.
To serve salmon, rinse fillet and pat dry. Place skin-side-down on cutting board and, beginning from the widest corner, slice into thin slices with a very sharp knife, leaving skin behind.
Arrange slices atop toasts. Finish each with a small dollop of crème fraîche and sprig of dill. Serve immediately, and with green salad if serving as a plated appetizer.