Melt the butter in a medium-size saucepan over medium heat. Add the flour to make a roux. Cook, stirring constantly, for 2-3 minutes, until lightly golden in color.
While roux is cooking, place the roasting pan that you cooked your turkey in on a burner over medium-high heat. Once the pan gets hot, add the wine and scrape up all the bits on the bottom of the pan with a wooden spoon. Add the bits to the roux along with the stock and season with salt and freshly ground black pepper.
Just before serving, beat an egg yolk in a small bowl with a ladleful of the gravy. Pour the egg yolk mixture back into the pot and mix it into the gravy to make it glossy and more stable.