Step 1
Dissolve yeast in 1 cup warm water in a small bowl. Let stand until yeast softens and begins to form a creamy foam about 5 minutes. Whisk in light corn syrup egg and vegetable oil.
Step 2
Whisk white rice flour brown rice flour potato starch tapioca flour salt xanthan gum and baking powder together in the bowl of an electric mixer fitted with a paddle or dough hook attachment. Pour yeast mixture into the bowl; mix on medium speed until well-combined 3 to 4 minutes. Add up to 2 tablespoons water if the dough is dry or crumbly.
Step 3
Turn dough out onto a work surface lightly dusted with rice flour and knead gently until smooth about 5 minutes. Transfer to a large greased bowl and cover with plastic wrap. Let rise until almost doubled in volume about 1 hour.
Step 4
Push down gently on the dough to deflate and separate into 12 equal pieces. Roll each piece into a rope about 15 inches long and shape into a \U.\ Twist the two ends of the dough and press them firmly into the top of the loop to form a pretzel shape.
Step 5
Preheat oven to 425 degrees F (220 degrees C). Generously grease 2 baking sheets.
Step 6
Bring 4 quarts of water to boil in a large pot. Add the baking soda and white sugar carefully; water will foam vigorously. Gently place one pretzel into the water bath; remove with a large slotted spoon when it floats to the top of the water and transfer to a dry baking sheet. Repeat with remaining pretzels. Transfer boiled pretzels to greased baking sheets brush with melted butter and sprinkle with pretzel salt.
Step 7
Bake in the preheated oven until pretzels are golden brown rotating the baking sheets halfway through baking about 25 minutes. Remove from the oven and allow to cool on a cooking rack.