Lobster Thermidor: The Classic

Ingredients

• 4 live lobsters, cooked only to just-done, flesh barely set
• For the béchamel
• 30 g unsalted butter
• 30 g plain flour
• 250 ml whole milk, warm
• For the sauce
• 200 ml lobster stock, reduced
• 150 ml double cream
• 2 tbsp Dijon mustard
• 1 tbsp fresh tarragon, leaves picked, finely chopped
• For the gratinée
• 40 g fine dried breadcrumbs
• 40 g Parmigiano-Reggiano, finely grated

Method

1. 1
   Cook the lobsters only to just-done. Split each along the length, remove the flesh from tail and claws, and set the cleaned shells aside. The flesh should be barely set at this point — it will receive further heat under the broiler.
2. 2
   Reduce the lobster stock in a saucepan until concentrated and deeply flavoured. In a separate pan, prepare a béchamel: melt the butter, stir in the flour, and cook briefly, then add the warm milk gradually, stirring until the sauce is smooth and coats the back of a spoon.
3. 3
   Combine the reduced lobster stock and the béchamel. Add the double cream and simmer until the sauce has a coating consistency. Remove from the heat, stir in the Dijon mustard and chopped tarragon. This is where the dish lives or dies: the mustard must be incorporated off the heat in a quantity sufficient to deliver the sharp, mustardy depth that defines Thermidor — too little and the preparation is anonymous; too much and it overwhelms the lobster.
4. 4
   Dice the reserved lobster flesh and fold it into the sauce. Spoon the mixture back into the cleaned shells, filling each evenly.
5. 5
   Preheat the broiler to its highest setting. Mix the breadcrumbs and grated Parmigiano and sprinkle evenly over the filled shells. Place under the broiler for 2–3 minutes. The surface is done when it is uniformly golden and the topping has set to a firm crust — the broiler must be hot enough to achieve this before the lobster beneath overcooks.