In a saucepan, over medium heat, melt 3 tablespoons of butter. Stir in the flour and cook for 2 minutes. Whisk in the stock, 1/2 cup at a time. Whisk until smooth. Season with salt and pepper. Bring the liquid to a boil and reduce the heat to low and cook for 15 minutes. Whisk in the cream and continue to cook for 2 minutes. Season with salt and pepper. Remove from the heat and whisk in the remaining butter. Serve warm.