15g (0.5 ounce; 1 tablespoon) sugar
10g (0.3 ounce; 2 1/2 teaspoons) Diamond Crystal kosher salt; for table salt use half as much by volume or an equal amount by weight
300g (10.5 ounces; about 1 1/4 cups) water
50g (1.75 ounces; 3 tablespoons plus 1 teaspoon) extra-virgin olive oil, plus extra for drizzling
400g (14 ounces) Stracchino cheese (a.k.a. Crescenza), divided (see note)
Coarse sea salt, such as Maldon or fleur de sel
Adjust oven rack to lower-middle position. Place Baking Steel or stone on it and preheat oven to highest possible temperature, 500° to 550°F (260° to 290°C). In a large bowl, whisk together flour, sugar, and salt until thoroughly combined. Add water and olive oil and stir with a wooden spoon until no dry flour remains and a shaggy dough forms, about 2 minutes. Knead with hands if needed to bring dough together. Let dough rest for 5 minutes. Turn dough out onto a floured surface and, using floured hands, knead until dough is mostly smooth and no longer sticks to your hands, 2 to 4 minutes. Dust work surface, dough, and hands with more flour as needed throughout the kneading process. Weigh dough, it should weigh approximately 900g (2 pounds). Divide into four total portions: two weighing 250g and two weighing 200g. Working with one portion at a time, cup dough between palms of your hands and work it in circular motions to form a smooth ball. Repeat with remaining dough. Cover dough with a clean kitchen towel or by overturning the bowl used to make the dough, or transfer to a lidded proofing container, and allow to rest at room temperature for at least 45 minutes and up to 1 hour. Alternatively, transfer dough balls to an airtight container and refrigerate for up to 24 hours. Lightly oil a 15-inch round pizza tray or rimmed baking sheet and place on top of a large bowl. Flour your work surface. Working with one 250g portion of dough, flour surface of dough and, using a rolling pin, roll into a 12-inch circle if using a round pizza tray or a 12- by 9-inch rectangle if using a rimmed baking sheet. While rolling, occasionally rotate and lift dough, adding more flour as needed, to ensure dough doesn't stick. Gently stretch dough into a 16- to 17-inch circle or 18- by 13-inch rectangle, about 1/16-inch thick, by draping over knuckles and gently stretching. Transfer dough to prepared pizza tray, stretching it so that there is an even 1- to 2-inch overhang of dough, then gently press it so that it is flush with the pan. Using clean hands or two spoons, dollop half of the Stracchino (200g; 7 ounces) in 1 tablespoon (15g) pieces over the surface of the dough. Using a rolling pin, roll out one 200g portion of dough in the same way as the previous portion. Gently stretch dough into a circle or rectangle (it should be thinner than the previous portion) by draping over knuckles and gently stretching. Place dough directly on top of the Stracchino-topped dough, stretching it so that it covers the entire surface, with a 1-inch overhang on all sides. Using your fingers, gently tear small openings in the top portion of dough, around the pieces of Stracchino. Gently press down on the top portion of dough, working around the pieces of Stracchino, so that it touches the bottom portion of dough. Hold the rolling pin at an angle, flush against the edge of the pizza tray, and work it around the entire edge of the tray to cut off the overhanging dough; excess dough can be saved for making more focaccia, or discarded. Drizzle surface of the dough with olive oil and sprinkle lightly with sea salt. Transfer tray to oven, positioning it on top of Baking Steel or stone. Bake until dough is deep golden brown and cheese is melted, rotating tray 180 degrees halfway through baking, 8 to 10 minutes. Remove from oven and transfer focaccia to a wire rack set inside a rimmed baking sheet. Allow focaccia to cool for at least 30 seconds, then transfer to a cutting board, slice, and serve immediately. Once tray or baking sheet is cool enough to handle, wipe clean with a paper towel. Repeat steps 5 through 9 with remaining portions of dough and Stracchino.