Pour 1/2 cup of the water into a bowl (preferably that of a stand mixer) and stir in the yeast and sugar. Let sit for 5 minutes, until it dissolves- if you're not sure of its age, make sure it gets foamy. (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 (or by hand) until well combined and shaggy. Continue to knead (I let the dough hook go for about 8 minutes, poking it down once in awhile) until it's smooth and elastic. (You could do this by hand, too.) If you used the dough hook, turn the dough out onto the countertop and knead a few times to make sure it's evenly smooth. Doesn't it feel great?
Shape it into a ball and put it back into the bowl. Cover with a tea towel 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 (love that part!) and pat each piece into a rectangle that's about 9x12 inches - or a bit bigger than a standard piece of paper.
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 with the tea towel again and leave them for an hour, until they puff right up out of the pan. As it rises, preheat the oven to 375°F, with the rack in the middle of the oven.
If you like, 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.