Strain the pan juices into a large heatproof jug. Use a metal spoon to skim as much fat as possible from the surface.
Place the roasting pan (used to roast your meat) over medium heat. Add the flour and use a fork to stir for 2-3 minutes or until the mixture bubbles. Gradually add 125ml (1/2 cup) of the wine and cook, scraping the pan with the back of the fork to dissolve any bits that have cooked onto the base, until the mixture returns to the boil.
Gradually add remaining wine, pan juices and stock to the pan, stirring with a wooden spoon until smooth. Boil gently for 10 minutes or until the mixture has the consistency of thin cream. Stir in pesto. Taste and season with salt and pepper. Pour into a warmed jug and serve immediately.