In the bowl of a stand mixer fitted with a dough hook, combine yeast, ½ cup of warm water, and sugar. Stir until well combined. Let stand for about 10 minutes or until nice and foamy.
In a separate mixing bowl, combine flour and vital wheat gluten. Set Aside. Add the remaining 1 cup warm water to the yeast mixture. Add the flour mixture. Mix until combined, about 4 minutes.
Add a little flour if necessary; You want it a little sticky, but not so much that it sticks to the sides of the bowl.
Cut up cold butter into little cubes and add to the mixing bowl. Add salt. Mix an additional 5-6 minutes, until butter is mixed in. Pull the bread off the hook if needed throughout the mixing process. Again, you want the dough to be slightly sticky and stretchy.
Grease a large bowl. Place dough inside and roll around a little to get it greased all around Cover and allow to rise in a warm place for about 1 hour.
Punch the dough down and divide into 3 equal pieces. (Flour your hands if the dough is too sticky, for easier handling.) Roll out each piece into a 12-inch-long loaf. The dough should be the same thickness all the way across. Place on a nonstick baking sheet, a baking sheet with a silicone baking mat, or a French bread baking pan. Cover and allow to rise for 40-60 minutes, until dough doubles in size.
Heat oven to 350 degrees F. Bake for 15-25 minutes (check at 15 minutes), until bread is golden brown. Remove from oven and lightly run a little cold butter over the top.
Allow loaves to cool completely, then serve with all your favorite sub sandwich toppings!