Lobster Thermidor — split cooked lobster, the flesh removed, mixed with a mustard and cream sauce and replaced in the shell, then gratinéed under a broiler — is one of the most theatrical preparations in classical French cooking and one of the most technically demanding. The complexity resides in the sauce (a béchamel-based preparation enriched with lobster broth, cream, and Dijon mustard) and the gratinée (the broiled Parmigiano-and-breadcrumb topping that forms a golden crust without overcooking the delicate lobster beneath).
- **The lobster:** Cooked only to just-done (the flesh should be barely set when removed from the shell) — it will receive additional heat during the gratinée. - **The sauce:** Reduced lobster stock + béchamel + double cream + Dijon mustard + tarragon. The Dijon is the Thermidor signature — it provides the specific sharp, mustardy depth that defines the preparation. - **The assembly:** Lobster flesh diced and combined with sauce — the mixture placed back into the cleaned shell. - **The gratinée:** Breadcrumbs and Parmigiano sprinkled over, placed under a hot broiler for 2–3 minutes until the surface is golden. The broiler must be very hot — to achieve the crust before the lobster overcooks.
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