Feed your sourdough starter 6-10 hours before preparing the dough.
In a large bowl, combine 345g of water, all the starter, and the flour. Mix until well incorporated. Cover and rest for 20-30 minutes.
After resting, add the salt and remaining 20g of water. Lightly knead for 1-2 minutes until the salt is fully incorporated.
Let the dough rest at room temperature for 30 minutes. After this, sprinkle the beet powder over the dough and perform a stretch and fold on all four sides.
Let the dough bulk rise for 4-5 hours at room temperature. During this time, perform a stretch and fold every 30-45 minutes. To do this, gently pull one side of the dough up and fold it over, rotating the bowl, and repeating on all sides. After the final stretch and fold, let the dough rest until it has nearly doubled in size.
After the final bulk fermentation, shape the dough and let it rest for 20 minutes on the counter.
Place the shaped dough in a proofing basket, cover with a towel, and allow it to rise at room temperature for 2 hours, or refrigerate for up to 72 hours.
Preheat the oven to 500°F (260°C) with a Dutch oven or a steam tray. Score the bread and bake covered for 20 minutes. Then reduce the oven to 400°F (200°C) and bake uncovered for another 30-35 minutes, or until the crust is dark brown.
Let the bread cool for 1-2 hours on a cooling rack before slicing.