In a large bowl, combine the water, yeast, sugar, and salt. Let it sit for 10 minutes until the mixture is bubbly.
Add half of the flour to the bowl along with 4 tablespoons of the butter. Combine until the flour is incorporated, then add the remaining flour.
Knead the dough for 10 minutes until smooth. If you are using a stand mixer, use the dough hook and mix for 5 minutes.
Spray a clean bowl with cooking spray and place the dough inside. Cover and put in a warm place for 1 hour. The dough should double in size.
Preheat the oven to 450 F.
Divide the dough into 8 pieces and roll each piece into a 24-inch rope. Take each rope and form it into a horseshoe shape with the open end at the bottom. Now cross the ends to create a small circle at the top with a couple of inches of the dough rope hanging down. Cross these loose ends and bring them up to connect with the top part of the circle and secure to form a pretzel shape.
Bring a large pot of water and the baking soda to a boil. Place each pretzel on a large spatula one at a time and lower them into the boiling water. Let them boil for 10 seconds and then set them on a parchment paper lined baking sheet.
Bake 12-14 minutes, until golden.
Melt the remaining butter and brush on the pretzels while they are warm. Sprinkle some flaky salt on each one and serve.