1. In a medium sized saucepan melt the butter.
2. Remove the pan from the stove and quickly stir in the flour.
3. Return the pan to the heat and cook the paste mixture, stirring frequently until it turns pale and straw-like in colour. This should take several minutes.
4. Take the pan off the heat again and whisk or stir in half of the stock. Make sure that the paste has dissolved and a liquid has formed without any lumps.
5. Return the pan to the heat and stir in the remaining stock. Bring the liquid to a gentle simmer.
6. Reduce the heat but continue to simmer the sauce for about 25 minutes, stirring from time to time and skimming off any skin that forms on the top.
7. Once the sauce has reached the desired consistency, season with salt and pepper and strain the sauce through a sieve.
8. Serve warm with your prepared dish.