Prepare the sweet levain by combining water, sugar, and starter in a medium bowl. Stir until the sugar is dissolved, then add the flour. Mix with a spoon until the mixture is even in texture.
In the bowl of a stand mixer, combine all-purpose flour, high-gluten flour, water, salt, and the sweet levain. Using the dough hook attachment, mix at medium speed until an even ball forms, about 5 to 7 minutes.
Transfer the dough to a lightly oiled bowl. Cover and let it sit at room temperature for 2 to 4 hours, performing 2 coil folds at 60 and 90 minutes.
Transfer the dough to the refrigerator and let it sit for up to 18 hours. If you plan to do this, keep the initial rise closer to 2 hours.
After the dough has rested, divide it into eight 130g pieces. Shape each piece into a tight, smooth round and place them on a lined baking sheet.