Have all ingredients at room temperature. Grease or oil 2 baguette pans.
Mix on low speed in a heavy-duty mixer bowl with the paddle attachment for 1 minute:
      1 1/4 cups white rice flour
      1 cup brown rice flour
      3/4 cup tapioca flour
      1/4 cup potato starch
      2/3 cup nonfat dry milk
      2 tablespoons sugar
      3 1/4 teaspoons xanthan gum
      1 tablespoon egg replacer
      5 teaspoons active dry yeast or quick-rising yeast
      1 1/2 teaspoons salt
      1/4 teaspoon ascorbic acid, or 1 teaspoon rice vinegar added with the liquid ingredients
Add and mix on low speed for 1 minute:
      1 large egg
      2 large egg whites
      1 1/2 cups warm (105° to 115°F) water
Increase the speed to medium-high and mix for 4 minutes. Spoon about half the flour evenly into each baguette pan and smooth the top. Brush the tops with:
      2 tablespoons melted butter
Cut 3 or 4 diagonal slashes about 1/2 inch deep across the top (unlike wheat-flour baguettes, this bread must be scored before it rises). Cover loosely with a clean kitchen towel and let rise at room temperature until puffy, about 35 minutes.
Preheat the oven to 350°F. Using a spray bottle, mist the baguettes with water and place in the oven. Bake 2 minutes and spray the baguettes again. Repeat a third time 2 minutes later. Bake until the loaves are golden brown, about 25 minutes more. Let the loaves cool in the pans for 10 minutes, then remove to a rack and let cool for 30 minutes before serving.