Lightly grease a baking sheet. Sift the flour and salt together into a large bowl and make a well in the center. Mix the yeast with the water in a small bowl

Gently warm the sour cream in a small pan until it reaches 98.6°F. Add to the yeast mixture and combine.

Add the yeast mixture and egg to the center of the flour and gradually mix into a dough. Beat in the softened butter.

Turn out onto a lightly floured surface and knead for 5 minutes, until smooth and elastic. Place in a lightly oiled bowl, cover with lightly oiled plastic wrap and let rise, in a warm place, for about 1-1/2 hours or until doubled in size.

Turn out onto a lightly floured surface and punch down. Cut in half and shape each piece of dough into a long rope about 14 inches in length.

To make the braid, place the two pieces of dough on top of each other to form a cross. Starting with the bottom rope, fold the top end over and place between the two bottom ropes. Fold the remaining top rope over so that all four ropes are pointing downward. Starting from the left, braid the first rope over the second, and the third rope over the fourth.

Continue braiding in this way to form a tapered bread. Tuck the ends underneath and place on the prepared baking sheet. Cover with lightly oiled plastic wrap and let rise, in a warm place, for about 40 minutes.

Meanwhile, preheat the oven to 375°F.

Mix the egg yolk and water for the glaze, and brush over the loaf.

Bake the bread for 30 - 35 minutes or until golden.

Cool on a wire rack.