Sauce Bercy — Shallot, Wine, and Fish Fumet Velouté

Ingredients

• For the reduction
• 4 shallots, finely minced
• 250 ml dry white wine, Muscadet or Chablis — minerally, not fruity, not oaky
• 250 ml fish fumet, well-made and clear
• 15 g unsalted butter
• For the velouté
• 300 ml fish velouté, blonde roux plus fish fumet, simmered 20 minutes
• To finish
• 60 g unsalted butter, cold, cut into small pieces
• 1 tbsp flat-leaf parsley, finely chopped

Method

1. 1
   Melt the butter for the reduction in a wide saucepan over medium heat. Add the minced shallots and sweat, stirring, for 3–4 minutes until fully translucent. The shallots must take no colour.
2. 2
   Pour in the white wine and fish fumet. Raise the heat to medium-high and reduce the liquid by two-thirds. This is where the dish lives or dies: the entire flavour of the finished sauce — the sweetness of the shallots, the acidity of the wine, the sea-mineral backbone of the fumet — is concentrated in this step. The finished reduction should measure approximately 150 ml of intensely flavoured liquid.
3. 3
   Add the 300 ml of fish velouté to the reduction. Simmer together over medium heat for 5 minutes to marry the flavours. The sauce should be pale gold and unified in character, with no separation between velouté and reduction.
4. 4
   Remove the pan from the heat entirely. Add the cold butter piece by piece, swirling the pan continuously between additions. The butter emulsifies into the sauce, giving it richness and gloss. The surface should appear smooth and sheening; any greasiness indicates the emulsion has broken.
5. 5
   Stir in the finely chopped flat-leaf parsley immediately before service. The finished sauce should be pale gold, glossy, with visible green flecks of parsley and occasional translucent shallot pieces. It should taste of wine and the sea — bright, clean, and savoury — with no trace of murkiness.