1/3 c. butter
1 Tb. flour
1/4 tsp. salt
1/2 c. boiling water
1 egg yolk
2 Tb. vinegar or lemon juice
Melt the butter, add the flour, salt, and water, and cook until the
mixture thickens. While still hot, pour over the slightly beaten egg
yolk, beating constantly to prevent curding. Add the vinegar or lemon
juice. Serve with vegetables that have been boiled in salt water.