If using active dry yeast, add sugar to water and sprinkle yeast into the sugar and water mixture. Mix and set aside.
Mix flour and salt together in a food-safe container.
Add water/sugar/yeast mixture to flour and salt in the food-safe container. Mix all ingredients together in the container to form a wet, sticky dough. Add more water if needed to achieve this consistency. (See video.)
Put a lid on the food-safe container and refrigerate.
The dough can remain in the refrigerator for up to one week. (See recipe notes below.) When ready to bake bread, remove 3 cups of dough from the container, leaving 1/2 cup of dough in the container. Proceed with the desired recipe to bake your bread of choice.
Refresh 1/2 cup of dough in the container by adding 3 cups of flour, 1 1/2 cups water, 1 tablespoon of sugar, and 1 teaspoon of salt to container. DO NOT add any additional yeast. Mix all ingredients together to form a wet, sticky dough. Add more water if needed to achieve this consistency. (See video.)
Put a lid on the food-safe container and refrigerate.
Repeat this process every week. At some point, you may decide to omit the sugar if you find that the dough has taken on a strong sourdough component and no longer needs the sugar boost.