Peel the cucumber, leaving alternating strips of green skin. Slice thinly and sprinkle with fine salt. Let it disgorge for 15 minutes.
Boil the vinegar with the sugar. Blot the cucumber slices dry, then drizzle with the hot vinegar mixture. Allow to cool, then stir in the whipping cream.
Rinse the salmon fillet briefly under cold water, then pat thoroughly dry with paper towels.
Lightly oil the fillet, focusing on the skin side. Place skin-side down on a wire rack or baking sheet. Position over ash-covered embers in the fireplace. Sprinkle with Guérande fleur de sel.
Cook for 10 to 15 minutes until perfectly done.
Transfer to a serving platter and season with white pepper. Garnish with dill sprigs and lemon slices. Serve the sweet and sour cucumbers on the side.
This method also works beautifully on a plancha.
