Combine the Water (1 1/2 cup), Kosher Salt (2 1/2 teaspoon) and Unsalted Butter (6 tablespoon) in the bowl of a stand-up mixer and sprinkle the Active Dry Yeast (1 package) on top. Let stand for 10 minutes, or until the yeast begins to foam.
Add the All-Purpose Flour (4 1/2 cup), using the dough hook, mix on low speed until fully incorporated. If the dough is too wet, add more flour one tablespoon at a time.
Increase mixer speed to medium and knead until the dough is smooth and pulls away from the sides of the bowl, approximately 4-5 minutes.
Transfer the dough to a large oiled bowl and cover with a moist tea towel. Let it sit in a warm place for 1 hour.
Preheat oven to 425 degrees F (220 degrees C) and line 2 half-sheet pans with parchment paper.
Bring a large pot of water and the Baking Soda (2/3 cup) to a rolling boil in a wide-mouth saucepan or roasting pan.
In the meantime, remove the dough from the bowl and place on a clean counter. If your dough is still a little sticky, lightly flour the surface. On the flip-side, if your dough is slightly dry, you may lightly oil the work surface.
Divide the dough into 8 equal pieces. With a moist tea towel, cover any dough you are not immediately working with.
Take one ball of dough, roll it out into a 22-inch rope using your hands. Making a U-shape with the dough, cross the right side over to the left, and left over to the right. Gently press the ends into the bottom of the U.
Transfer the pretzel to the parchment-lined baking sheet and cover with a damp tea towel while you work on the remaining pretzels.
Place the pretzels, 2 at a time, into the boiling water for 30 seconds, splashing the tops with a spoon. Carefully remove with a wide spatula or spider and return to the parchment-lined baking sheet to rest.
Beat Egg (1) yolk with 1 tablespoon of water. Brush each pretzel with the egg wash. Sprinkle with Sea Salt (to taste) just before transferring them to the oven. Place in the oven and bake for 15 to 18 minutes.
Transfer to a cooling rack for at least 5 minutes before serving.