In a small pot over medium heat add butter and stir until melted. Sprinkle flour and salt in pan and whisk together with the butter. Cook flour and butter for about 1 minute or until the flour and butter become fragrant. Add about 1/2 of the milk and stir until the mixture becomes thick. Add the remaining milk and stir until the mixture becomes thick. Add chopped egg, reserving some of the chopped egg for garnish. Pour sauce over toast and garnish with remaining chopped egg.