Line a mini pullman loaf pan (half loaf size - linked under equipment) with parchment paper and lightly grease it.
In the bowl of a stand mixer, whisk to combine the Caputo Fioreglut gluten-free flour blend, dry milk powder, and kosher salt.
In a separate bowl, whisk together the gluten-free sourdough starter, warm water, melted butter, and honey until well combined.
Pour the wet mixture into the dry ingredients in the stand mixer bowl.
Using the paddle attachment, blend the mixture on medium speed for 2-3 minutes until a smooth batter forms. The dough will be thick and sticky.
Spread the batter into the prepared loaf pan, smoothing the top with a spatula.
Cover the pan with a plastic wrap or a bowl cover and set aside in a warm spot. Let the dough ferment for 5-7 hours or until the dough has about doubled in size.
When ready to bake, preheat the oven to 350°F. Place the bread in the preheated oven and bake for 50 minutes, or until the top is deep golden brown and the center of the loaf reaches at least 205°F.
Remove the bread from the oven and let it cool in the pan for about 10 minutes before transferring it to a wire cooling rack to finish cooling. Let rest for at least 2 hours before slicing.
Notes
Double check the size of your pan. This recipe is for a mini-pullman loaf pan. My pan measures 4 inches (width) x 4 inches (height) x 4 inches (depth).
Be patient. Sourdough loaves take a very long time to rise. For several hours it may appear as if nothing is happening. My loaves typically take about 5-7 hours to fully double in size.
Double the recipe for a full-size loaf of bread. Keep an eye on the bread as a full loaf may take a bit longer to bake.
Make sure your kitchen is warm enough. If your house is cold, the bread may take much longer to rise. A seed starting mat or bread proofing box may be helpful if your house is chilly, especially during the winter months.