Electric mixer method

Use 4-day-old double cream and put it into the mixing bowl. Use the heavy beater on the mixer, and run it on low speed. The cream will whip and then become very thick and curdled looking. As soon as this happens, reduce the speed to the lowest setting and continue until the butter forms one lump. Drain off the buttermilk. Wash the butter in cold water until the water remains clear. Squeeze well to extract water and then add salt to taste before patting the butter into shape. 1 pint/500ml cream is a practical quantity to deal with.