In a large mixing bowl, mix the two types of flour, yeast, and salt. Add water and mix the dough at high speed using the whisk attachment until the dough no longer sticks to the sides and bottom of the bowl. Scrape the soft dough off the whisk, put a lid on the mixing bowl, and let the dough rest in the fridge overnight.
The next day, remove the dough from the fridge and allow the dough to warm for a couple of hours before continuing.
Gently turn the dough onto a generously floured work surface, and dust the top of the dough with a little flour. Divide the dough into two equal-size pieces. Quickly twist the pieces together, preserving as much air in the dough as possible. Place the twisted loaf on a peel lined with parchment paper. Let proof until nearly doubled in volume.
Put baking stone in the oven and preheat to 450°F.
Mist the loaf with water. Ease the loaf, along with the parchment paper, onto the baking stone. Spray a little water into the oven. Repeat after one minute.
After 5 minutes of baking, lower the heat to 400°F, then bake the loaves for another 20-30 minutes more.