1. To make the pre-ferment starter: Stir the flour, water, and yeast together in a small bowl until combined. Cover with plastic wrap and let sit overnight at room temperature.
2. To make the dough: Add the pre-ferment, flours, water, oil, dry milk, salt, and yeast to the bowl of stand mixer. Mix on low with the paddle attachment just until the mixture is combined. Let the mixture rest for 45 minutes (no need to cover).
3. Switch to the dough hook and knead on low speed for 10 minutes. The dough will be very soft and sticky so don’t be tempted to over-knead it – it will not come together in a ball like other recipes do. Using a plastic dough scraper or silicone spatula, scrape the dough into a well-oiled bowl, cover with plastic wrap, and let stand at room temperature for 3 hours. After each hour, gently deflate the dough and recover (3 times total).
4. After the last deflation, let the dough rest for 10 minutes while you line two baking sheets with parchment paper. Split the dough in half and gently stretch one half of the dough out in your hands to about 10 inches long. Place it on one of the baking sheets and pat it into a 12-inch long by 3- or 4-inch wide shape. Repeat with the remaining dough, placing that piece on the second baking sheet.
5. Generously grease two long pieces of plastic wrap and lay a piece loosely over each loaf. Allow the dough to rise for 2 hours at room temperature until very puffy. Towards the end of the rise time, position a baking stone on the bottom rack of the oven and preheat the oven to 425° F.
6. Remove the plastic wrap and transfer the loaves on the parchment to the preheated baking stone. (If you don’t have a stone, bake the loaves directly on the baking sheets.) Bake for 20-25 minutes, rotating after 10 minutes, until the loaves are browned and the internal temperature reads at least 205° F on an instant read thermometer. Transfer the loaves to the oven rack, prop the door open, and allow the loaves to cool slightly (or completely) before slicing and serving.

Storage: The ciabatta is best served the first day it’s made but since this recipe yields two large loaves, I recommend baking both and freezing what you don’t eat within one day, rather than trying to halve the recipe. No one ever cried about having extra homemade bread in the freezer!