Gather the ingredients so that you have everything on the counter or table.
Prepare the Dough
In a large mixing bowl, combine the active sourdough starter, water, instant yeast, granulated sugar, kosher salt and 3 cups of all-purpose flour.
Mix with a dough hook until well combined. Gradually add remaining flour until mixture forms a ball.
Knead by machine or by hand to form a smooth dough, 3-5 minutes.
Place dough in a greased bowl and cover with plastic wrap. Allow the dough to rise until it has doubled. (About 60-90 minutes with yeast; 2-3 hours without.)
Form the Baguettes
Once the dough has doubled, divide the dough into fourths. Pat out into a rectangle and roll to shape each into a 12-15" baguette. Pinch edges and ends to seal seam. Rub brown rice flour over baguettes to coat. Place two loaves on a baking sheet lined with parchment paper or a silicone baking sheet. Repeat with all four pieces.*You may also opt to use a baguette pan or baker, if you have one.
Cover and allow to rise until puffy, about 90 minutes to 3 hours, depending on use of yeast and how active your sourdough starter is.
Bake Baguettes
Before baking, make three deep diagonal slashes with a bread lame or sharp knife on each loaf. Spray the baguettes with warm water right before placing in oven.
Bake in a preheated 425°F oven for 25-30 minutes or until crust is a deep golden brown. Turn oven off, and leave bread in oven for 10 minutes with the door ajar. This will help make the crust extra crispy.After ten minutes, remove baking tray from oven and cool loaves on a wire rack. Makes four loaves.
Notes
*If you've opted not to use yeast, work the dough at each thirty-forty minute interval to stretch and fold the dough, envelope-style to work the gluten. The dough will most likely be sticky. Use a stainless bench scraper to lift the dough from the work space, as needed . Try not to use additional flour, as this will affect the light airiness of the bread.**For best freshness without compromising the crispiness of your crust, store bread in a sealed paper bag.