Dissolve yeast in warm water.
Stir in lukewarm water, the sugar, salt, 1 egg, the shortening and 1 1/4 cups of the flour.
Beat until smooth.
Mix in enough remaining flour to make dough easy to handle.
Turn dough onto lightly floured board; knead until smooth and elastic, about 5 minutes.
Round up dough in greased bowl; turn greased side up.
Cover; let rise in warm place until double, 1 1/2 to 2 hours.
Punch down dough; divide into 3 equal parts.
Roll each part into strand, 14 inches long.
Place strands close together on lightly greased baking sheet.
Braid gently and loosely.
Do not stretch.
Fasten ends; tuck under securely.
Brush braid with shortening.
Let rise until double, 40 to 50 minutes.
Heat oven to 375Â°.
Beat egg yolk and cold water until blended; brush over braid.
Bake 25 to 30 minutes.