Stir sugar into warm milk and sprinkle with yeast.
Let stand 5 minutes or until the surface is frothy.
Stir gently to moisten any dry particles remaining on top.
Sift flour and salt into a large bowl.
Melt butter or margarine; cool slightly.
Lightly beat butter or margarine and 1 egg into yeast mixture.
Pour into flour mixture, combining to make a dough.
On a floured surface, knead dough until smooth and elastic.
Cover and let rise in a warm place until doubled in size.
Divide risen dough into golf-ball size pieces and shape into balls.
On a floured surface, roll out each ball into a triangle with sides about 6 inches (15 cm) long.
Press point of each triangle firmly onto a baking sheet.
Starting at the long side opposite the point, roll up triangles using both hands.
Seal points of triangles to rolls with a little egg yolk.
Curve each roll into a crescent.
Arrange on baking sheet; brush with beaten egg yolk.
Cover and let rise in a warm place 15 to 20 minutes.
Preheat oven to 450°F (230°C).
Bake crescents 10 to 15 minutes or until golden.