In a large bowl, whisk the starter, water and sugar together with a fork. Add the flour and salt. Combine to form a rough dough, then finish mixing by hand to fully incorporate the flour. Because this dough is stiff, consider using a stand mixer (fitted with the dough hook attachment) to give your hands a break; run on low speed for 5-6 minutes to combine. Cover the dough with a damp towel and let rest for 45 minutes to 1 hour. Meanwhile, replenish your starter with fresh flour and water. Store according to preferences. After the dough has rested, work the mass into a semi-smooth ball, about 15-20 seconds and place in a large bowl that’s lightly oiled.