First make some ravigote butter by chopping a clove of garlic and a shallot finely, make it up to 2 tablespoonfuls with mixed herbs, and beat the mixture into 2 tablespoonfuls of butter.
Then separately melt 5 tablespoonfuls of butter, stir in 3 tablespoonfuls of flour, to make a white roux.
Add | of a glass of stock and 1 tablespoonful of vinegar, stir it in until the sauce thickens, season with salt and pepper, and let it boil for 5 minutes.
Then stand the saucepan in a dish of hot water, away from the heat, and add the ravigote butter and beat as the butter melts.
If this is done on a direct heat the sauce will be spoiled.