In a large bowl, whisk together the bread flour (4.25 cups) and instant yeast. Add the 1.5 cups water and mix with a spoon or hand until a shaggy dough forms, 1–2 minutes. Cover and rest 10 minutes.
Sprinkle in the fine sea salt and knead until smooth, elastic, and slightly tacky, 8–10 minutes by hand or 6–8 minutes on medium speed in a mixer. Form into a ball.
Place the dough in a clean bowl, cover, and let rise at warm room temperature until doubled in size, 60–75 minutes. The dough is ready when a floured fingertip indentation springs back slowly and not completely.
Lightly dust the work surface with some of the 0.25 cup bread flour for dusting. Turn out the dough and divide into 12 equal pieces (about 75 g each). Shape each into a tight ball, cover, and rest 10–15 minutes to relax.
Make the marraquetas: Pair two balls and press them together to form a single oval. Using the handle of a wooden spoon or a thin dowel, press a deep groove lengthwise down the center all the way to the surface, then rotate 90° and press a second deep groove to form a cross, creating four lobes. Transfer to a parchment-lined sheet. Repeat with remaining pieces to make 6 rolls.
Cover loosely and proof until noticeably puffy and lighter, 45–60 minutes. Just before baking, firmly press again along the same grooves to re-mark the cross so the quarters separate well in the oven.
Meanwhile, place a baking stone or inverted heavy sheet on the middle rack and an empty metal pan on a lower rack. Preheat the oven to 475°F for at least 30 minutes.
Slide the parchment with the rolls onto the preheated stone/sheet. Carefully pour the 1 cup very hot water into the lower pan to create steam and close the door. Bake 12–15 minutes, until well risen and deep golden.
Remove the steam pan, rotate the tray, and bake 5–8 minutes more, until the crust is richly browned, blistered in spots, and the bottoms sound hollow when tapped. For extra crispness, turn off the oven, prop the door slightly, and leave the rolls inside 3–5 minutes.
Cool on a rack at least 20 minutes before serving to set the crumb and crisp the crust.