Warm the milk (to 110 degrees F); add to mixer with butter, sugar, and sourdough starter.
Add the flour and mix well until the dough forms a soft ball. Turn out onto a lightly floured counter and knead for 2-3 minutes. Then form the dough into a smooth ball of dough and place into a lightly-oiled bowl.
Cover with plastic wrap and allow to rest/rise for 2 hours.
Once the dough has risen, turn out onto a lightly floured counter. Punch the dough down and knead lightly for a brief minute or two. Then separate the dough into 12 equal pieces.
Roll out each piece into a long strip 26-30" in length. If you are slow to roll out the pieces, then cover the balls of dough with a damp cloth to prevent them from drying out.
Once the dough strips have been rolled out, shape them into a pretzel and place them on a parchment-lined cookie sheet. You will need to use 2-3 cookie sheets.
Place the cookie sheets in the freezer for 20-30 minutes. The goal is to allow the pretzels to harden just enough that they can be dunked in the water bath.
With the pretzels in the freezer, preheat the oven to 450 degrees F. Fill a large gallon stockpot 3/4 of the way with water; bring to a strong simmer. Add 1 tbsp baking soda allow to dissolve.
Remove the pretzels from the freezer; add them to the water (4 at a time), and allow to simmer until they float to the top. Gently remove from their bath and place back on the cookie sheet.
Brush with a beaten egg and sprinkle with your choice of toppings. Bake at 450 degrees F for 14-15 minutes until lightly brown. They will be hard when tapped (but will soften as they cool).
Remove and allow to cool before enjoying.