Pour 1/2 cup of the water into the bowl of a stand mixer fitted with a dough hook. Stir in the yeast and sugar. Let sit for 5 minutes, until it dissolves and begins to foam. (If the yeast doesn't do anything, toss it out and buy fresh yeast.)
Add the rest of the water and about half of the flour. Stir until well blended. Add the rest of the flour, the salt and butter and stir with the dough hook until well combined and shaggy. Continue to knead for between 5-10 minutes until it's smooth and elastic. Turn the dough out onto the countertop and knead a few times to make sure it's evenly smooth.
Shape it into a ball and put it back into the bowl. Cover with a plastic and let it sit for 1 - 1 1/2 hours, until it's doubled in size.
Butter two 9x5-inch loaf pans, or line them with parchment. Punch the dough down and pat each piece into a rectangle that's about 9x12 inches.
Starting at a short end, fold it in thirds, like a letter. Place seam side down in the loaf pans, tucking the ends in. Cover and leave them for an hour, until they puff right up out of the pan. As it rises, preheat a conventional oven to 375°F, with the rack in the middle of the oven. (350*F in a convection oven).
Brush the tops of the loaves with milk before baking. Bake for 30-35 minutes, until the loaves are honey brown. Immediately turn the loaves out of their pans and onto a rack to cool.