Mix the dry ingredients together in a large bowl.
Dissolve the sugar into the body temperature water, and add yeast to proof.
Heat the milk and butter together, to 120-130℉ / 50-55℃. I microwaved it in a cup for around a minute.This should feel very warm to the touch, but not actively burn you. Wet ingredients ready to go!
Pour the hot milk mixture onto the dry ingredients, and stir it in. Then add the yeast, sourdough starter, and egg.
Beat for a minute or two, until you have something like a cohesive sticky thick cake batter. Add a little more lukewarm water if required.
Butter the loaf pan, and lightly coat the inside with cornmeal.
Scrape the batter into the pan, and even it out. I tapped mine on a counter to level the surface out and knock out any air gaps.
Cover the pan, and let sit in a warm place for around 30 minutes or until it has risen about halfway.
Start the oven preheating to 200℃ / 400℉. I put in the baking stone again, as detailed on the recent Gluten Free Sourdough Beer “Rye” Bread. Let the dough continue to rise until it has roughly doubled in size. Brush the top with melted butter.
Bake for 25-35 minutes, or until the top is golden brown and the internal temperature reaches 208-212℉ / 98-100℃. My loaf took closer to 40 minutes using a temperature probe, but that was in a deep Pullman pan. Remove from the pan after 5-10 minutes of cooling, and let the loaf finish cooling on a rack.
When it's cooled completely, slice in and enjoy!