Place the salmon in a bowl and add the lemon juice. Stir, then cover and leave for 10 minutes, stirring after 5 minutes.

Meanwhile, add the olive oil to a small skillet and place over a medium heat. Add the shallot and garlic, and cook until the shallot is tender. Divide the mixture between two large ramekins or two small baking dishes.

Preheat the broiler.

Drain (and discard) the juice from the salmon, and add the heavy cream, tarragon, salt and pepper. Stir well, then spoon the mixture on top of the shallot.

Finally, sprinkle the Swiss cheese over each dish and place under the broiler (one rack down so not too close) until the cheese has melted and has turned golden brown.