Combine flour, salt, yeast, and sugar; add oil: In a large bowl, whisk together flour, kosher salt, yeast, and granulated sugar. Add water and stir until a sticky, ragged dough forms. Transfer dough to another large bowl drizzled with 3 tablespoons oil, turning to evenly coat.,

Refrigerate until doubled in volume: Cover and refrigerate until the dough doubles in volume, at least 12 hours or up to 3 days (punch down dough each time it doubles in volume until ready to use). Or let the dough proof at room temperature, 2 to 3 hours.,

Turn and fold dough: With dampened hands, lift bottom of dough in bowl up over itself and press into center of dough. Turn the bowl 90 degrees, then lift and fold the dough again in the same manner. Repeat this turning and folding process until the dough becomes a taught and smooth ball and most of the excess air has been removed.,

Cover and let stand: Cover and let stand at room temperature until doubled in volume again, about 1 hour (closer to 2 hours if dough was refrigerated).,

Preheat oven, prep pan: Preheat oven to 500°F with rack in center position. Coat the bottom of a 9-by-13-inch rimmed baking sheet or shallow pan with 3 tablespoons oil.,

Press dough into pan; cover and let sit: Pour dough into pan, pressing evenly to the edges with your fingers. Cover and let sit 20 minutes.,

Make indentations and sprinkle with cranberries: Make deep indentations all over dough with fingers, then sprinkle evenly with cranberries, rosemary, and sanding sugar; drizzle with 2 tablespoons oil.,

Bake and serve: Bake until focaccia is golden on top and bottom and just cooked through, about 15 minutes. Serve warm, sprinkled with flaky salt.