Beat the buttermilk, butter and egg lightly in a bowl.
Mix the flour, baking soda, sugar and salt together and add them all at once to the buttermilk mixture, stirring just enough to moisten the flour.
Lightly butter or grease a griddle or frying pan and set over moderate heat. Pour about 1/4 cup per pancake on the griddle; cook until the cakes are very bubbly on top and the underside is lightly browned. Turn with a spatula and brown the other side.
Place finished buttermilk pancakes on a heated plate in a very slow, 200°F oven until ready to serve.