In small pot, heat 1/2 cup nondairy milk (or microwave) until warm to the touch but not scalding. In heat-proof bowl, add yeast and sugar, then pour milk overtop. Set aside for 15 minutes.
In stand mixer or large bowl, whisk tapioca starch, cornstarch, flour, psyllium, and salt. Add melted butter or oil, remaining 1 1/2 cups nondairy milk, and yeast mixture. Use dough hook or hand mixer on low speed to beat until just combined.
Shape dough into a ball. Transfer to lightly oiled bowl, cover with dish towel and set in a warm, draft-free place for 90 minutes.
Preheat oven to 400 F.
In medium pot, bring 5 cups water to a simmer with baking soda. Line 2 baking sheets with parchment paper. On cutting board or clean countertop, divide dough into 10 pieces and roll into 15 in strands. Push edges away from you into a “U” shape and twist the ends over each other twice (there are plenty of videos online for this if you need help). Then bring the ends down to the bottom of the “U.”
Remove pot of water from heat. Using large, flat spatula, carefully pick up and slide a pretzel into water for 30 seconds. If water doesn’t cover the pretzel, rotate pot to submerge. Remove pretzel to parchment-lined baking sheet and repeat with remaining pretzels. You can do this all at once, but the pretzels are delicate.
Sprinkle pretzels with coarse salt and bake for 15 to 20 minutes, until golden brown.
Enjoy!