In a stand-mixer or hand-held mixer with dough-hook, whisk plain yogurt and water until even. Add bread flour, buckwheat flour, sea salt and instant dry yeast, and mix on low until incorporated, then turn to medium-high speed and knead for another 12~15 minutes. The dough will be very wet in the beginning, sticking everywhere, but it will eventually (in the last few minutes) develop enough gluten to pull away completely from the sides and bottom of the bowl, and become very silky, shiny and elastic. When the machine stops, the dough will stick right back to the bowl, but should pull again cleanly when you scrape it with a spatula. This will be very hard to achieve by kneading with hands, but you're welcome to try.

Cover the bowl and let rise at room-temperature until fully doubled, about 1:30 to 2 hours.Alternatively, you can let the dough rise in the fridge for 24 hours or until doubled.

Preheat the oven on 570 F/300 C with fan-on (or as high as your oven can go which is sometimes 500 F/250 C). Rub a little oil on a large baking sheet and stick a piece of parchment paper on top. Generously dust the entire parchment paper with flour, then scrape the dough on top. Gently fold ⅓ of each side the dough over itself into a rectangular shape, like folding a letter (the long side should be the same as the baking sheet). Generously dust flour on top of the dough and cover loosely with a piece of plastic wrap (be generous with flour because we don't want the dough to stick to the plastic!). Let rise again for 45 minutes to 1 hour until doubled again. If your dough rose in the fridge, it may take longer like 1:30 to 2 hours.

Remove the plastic wrap (be careful because some small areas might stick). Use the middle knuckles of your fingers to GENTLY dent and push the dough outwards towards all four directions, keeping the air bubbles inside and dusting with flour as needed, until the dough is about ¾" (2 cm) at its thickest part. Now use the middle knuckles again to make random punctures 2" (5 cm) apart that goes all the way through the dough to the pan. This will prevent the dough from doming too much while baking. With a spray bottle, spray a thin mist of water all over the dough and the baking sheet (helps crust forming), then drizzle extra virgin olive oil on top of the dough.

Bake in the middle rack of the oven for about 12~17 minutes, until the crust is deeply browned and blistered. I like to use a blow-torch to further char the surface of the bread when it comes out of the oven. Let cool on a cooling rack for 30 minutes.

A suggestion for sandwich: Burrata + mortadella + prosciutto + baby arugula + clotted cream + dust of black pepper.