Dissolve sugar in water in a 2-cup measuring cup; gently stir in yeast. Let stand until yeast softens and top is foamy, about 5 minutes.

Whisk 3 3/4 cups flour and salt together in a large bowl; make a well in the center. Pour yeast mixture into well; stir gently, starting from the middle, until a sticky dough forms. Turn dough out onto a lightly floured surface; knead, adding more flour if needed, until dough is elastic and no longer sticky, about 10 minutes.

Oil a large bowl; add dough and turn to coat. Cover with a towel and let rise in a warm place until doubled in volume, about 1 hour.

Preheat the oven to 425 degrees F (220 degrees C) with one rack in center position and one rack in lowest position.

Fill a roasting pan with water; place on lower rack. Line a baking sheet with a silicone mat.

Punch down dough and turn onto a lightly floured surface. Form into 1 large loaf (or 6 sandwich loaves), tapering the end(s). Place loaf (or loaves) on the prepared baking sheet. Cut 3 or 4 diagonal slashes, about 1/4- to 1/2-inch, across top(s). Cover with a dry towel and let rise until doubled in volume, about 40 minutes.

Uncover loaf (or loaves); bake in the preheated oven on the center rack until top is light golden brown, 15 to 20 minutes depending on size of the loaves.