Prawn Bisque Base

Heat the butter and olive oil together in a large, heavy-bottomed pot over high heat until the butter foam subsides and the fat is very hot — nearly smoking. Add the prawn shells and heads in a single layer. Do not stir for the first 2 minutes. You are looking for the Maillard reaction to occur on the shell surface, creating the toasted shellfish flavor that is the soul of bisque. After 2 minutes, stir and toss vigorously for another 3-4 minutes until the shells are uniformly bright orange-red and the kitchen smells intensely of roasted crustacean.

Add the tomato paste directly to the shells and stir vigorously to coat every shell with the paste. This technique — called pinçage in classical French cooking — involves frying the tomato paste in the shell fat for 2-3 minutes until it darkens from red to a deep brick-orange and sticks in places to the pot bottom. The acidity of the tomato paste cooks off, leaving concentrated sweetness that reinforces the shellfish sweetness.

Pour the cognac into the pot and stir vigorously — the alcohol will immediately lift the fond from the bottom. If you have a gas flame, tip the pan slightly and allow the cognac to flame briefly (flambé), which burns off the harshest alcohol edge while preserving the brandy complexity. Allow the flame to die naturally, then add the white wine. Reduce the wine by half over high heat, about 5 minutes, stirring occasionally. The liquid should smell of shellfish, toasted cognac, and a faint marine sweetness.

Add the shallots, celery, carrot, and garlic to the pot and stir. Add the fish stock, bay leaf, tarragon, and cayenne. Bring to a simmer and cook for 25-30 minutes. Do not boil aggressively — shellfish stocks become bitter under a rolling boil. The broth should be a rich, warm orange-coral. At 25 minutes, taste: it should be intensely savory, sweet from the shellfish, and warmly spiced from the cayenne.

Remove the bay leaf and tarragon sprigs. Working in batches (or using an immersion blender), blend the entire contents of the pot — shells, vegetables, and broth — on high speed for 2 minutes per batch. The shells will break down into small fragments. This step extracts the last collagen and chitin from the shells and gives the bisque its characteristic opaque, velvety body. Blend thoroughly.

Strain the blended bisque through a fine-mesh sieve, pressing firmly with the back of a ladle to extract as much liquid as possible from the shell pulp. Discard the dry shell paste. Return the strained liquid to a clean saucepan. Add the heavy cream and bring to a gentle simmer. Reduce over medium heat for 10-15 minutes, stirring occasionally, until the bisque has thickened to a consistency that coats the back of a spoon and the colour has deepened to a rich, coral-salmon. Season with salt. Taste and adjust — bisque should be lush and intensely flavored, slightly sweet from the shellfish and cream.