1. For the shrimp sauce: melt 40 g of butter in a frying pan over low heat, add flour, remove from heat and mix well. Return to the heat and cook, stirring constantly, for 4-5 minutes, so that the mixture turns the color of hazelnuts (this base for sauces in French cuisine is called "roux"). Pour in the fish broth three times and whisk until it is completely absorbed into the oil mixture and flour. Cook on low heat for 30 minutes, stirring occasionally.