Preheat your oven to 450 degrees. Do it now so that your oven is nice and hot when you put the bread in.
In a large bowl or stand mixer, combine warm water, sugar, yeast, and salt. You want the water to be like a nice warm bath water. Feel it with your wrist.
Set your bowl on the preheating oven and wait a couple minutes. If you see bubbles from the yeast reacting, move forward. If not, you may have killed your yeast with too hot water. Dump it and start over!
Add the softened butter and 1 cup of flour, and stir together with a wooden spoon.
Use the dough hook (or continue with the wooden spoon) to stir in the rest of the flour. Start with 3 cups total in the recipe (including the cup you added in step 4). Then add the last cup 1/4 cup at a time to see how much you need. The dough should be pulling away from the sides of the bowl but still sticky. (see photos) I usually add most of the fourth cup.
Knead for 6-7 minutes, until the dough is smooth and elastic.
Prepare a baking sheet or baguette pan** with nonstick spray.
At this point you can either shape the dough into one large loaf that is about 12-14 inches, or you can make 2 smaller loaves. (I made two smaller loaves to fit in my baguette pan.)
Use a sharp serrated knife to make 3-4 half-inch slits on top.
Cover with a tea towel and let rise for 20 minutes.
When the loaf or loaves have roughly doubled in size, remove the towel.
In a small bowl, use a fork to whisk up 1 egg white. Make it nice and frothy. Use a pastry brush to coat the tops and sides of the bread. You can use all or most of the egg white.
Transfer the bread to the oven.
Bake for about 20 minutes. You will know it is done when the top is shiny and golden, and the bottom of the loaf is browned. The longer you leave it in, the crispier your crust will be.
Let cool for a bit and then devour hot with butter!