In the bowl of a stand mixer, combine the yeast, sugar, 3 ½ cups of the flour and salt.
Add the softened butter, then add the hot water gradually to the flour mixture, stirring until well mixed. Dough should still be pretty soft at this point.
Attach the dough hook and begin kneading. At this point, start adding the remaining flour 2 tablespoons at a time and keep adding until dough no longer sticks to the side of the bowl as it's kneaded. knead for about 8 minutes.
Transfer dough to an oiled bowl and turn so that dough is lightly coated with oil. Cover and let rise for one hour.
After dough has risen, divide it into 10 pieces.
Preheat the oven to 450 degrees F.
Bring the water and baking soda to a boil in a large saucepan.
Roll out each piece of dough into a 24-inch rope and shape into a pretzel shape directly on nonstick foil or parchment lined baking sheet.
Working one piece at a time, put the shaped pretzel in the boiling water for 30 seconds, then lift it out with a slotted spatula and return to lined baking sheet.
When all pretzels are formed, brush with the egg yolk mixture and sprinkle with salt.