In a large mixing bowl (or using a stand mixer with a dough hook), stir together the water, sugar, and salt until the sugar is dissolved. Sprinkle yeast over the top and allow to sit for 5 minutes.
Add the flour to the bowl and stir consistently adding the butter in a slow drizzle.
Knead the dough on a floured surface for 5 minutes or until a smooth ball forms.
Grease a clean bowl with oil and transfer the dough to the oiled bowl. Cover with a clean tea towel and rest in a warm spot, free of drafts, for 1 hour or until doubled in size.
Preheat oven to 450 degrees. Line a baking sheet with parchment paper and spray with cooking spray.
Fill a large stockpot about halfway with water, add baking soda and bring to a boil.
Meanwhile, grease a clean surface lightly with oil. Divide dough into 8 to 10 equal portions. Roll out each dough portion into a rope about 24 inches long.
Twist dough into pretzel shape by creating a U. Twist loose ends together and fold the twist back over to the middle of the U and press together.
One at a time, drop pretzels into the boiling water and allow to boil for 30 seconds. Remove using a slotted turner and immediately place on the prepared baking sheet.
Mix together water and egg yolk. Brush over pretzels and immediately sprinkle with kosher salt.
Bake for 12 to 14 minutes or until the pretzels are golden brown.
Whisk together the mustard ingredients and serve with warm pretzels.