Combine 1 1/4 cups flour, sugar, salt, and yeast in a mixer.

Mix in the softened butter.

Stir the saffron into the warm water until it dissolves.

Add a little at a time to the flour mixture and blend thoroughly. (If using saffron threads, use a fine sieve to filter out the saffron.)

Beat for two minutes at medium speed, scraping the bowl occasionally.

Separate the yolk and white of 1 egg.

Blend the single egg white and the other three whole eggs into the batter.

Reserve and refrigerate the single egg yolk.

Stir 1/2 cup of flour into the batter and beat at medium-high speed for 2 minutes, scraping the bowl occasionally.

1/2 cup at a time, blend in enough additional flour to make a soft dough (4 to 5 cups total).

Knead the dough on a lightly floured board (or in the mixer, with a kneading hook) for twelve minutes, or until it is soft and elastic (the longer you knead the dough, the more dense and cake-like the bread will be).

Place the dough in a greased bowl, turning it once to grease the top.

Cover and allow the dough to rise in a warm, draft-free place until doubled in bulk (approximately 1 hour).

Flour a pastry board lightly and set the dough on it.

Divide the dough into three equal portions.

Roll each of these portions into a rope approximately 15 inches long.

Braid the lengths together tightly, using the fingers to pinch the ropes together at the ends.

Place the braided loaf on a greased baking sheet.

Mix the reserved egg yolk with 1 teaspoon cold water and brush the tops of the loaves with this mixture.

Sprinkle liberally with poppy seeds, and let the loaf rise until doubled in bulk in a warm, draft-free place (approximately 1 hour).

Bake in a preheated 400° oven for 20 to 25 minutes.

Remove from the oven and cool on wire racks.