Combine the yeast and 2 cups warm water in a mixing bowl and stir to dissolve. Add the butter, sugar and salt. Use a wooden spoon to stir in one-third of the flour until smooth. Add another third of the flour and stir, then turn it out onto a floured board to knead. Knead it over 15 minutes, adding the rest of the flour as you knead. Don't let it get dry too fast; it should stay sticky. Put the dough in a buttered bowl and cover with plastic wrap. Let it rise for 1 hour.
Knead the dough another 5 minutes, place it back in the bowl and let it rise another hour.
Butter 2 loaf pans. Shape the dough into 2 loaves and transfer them to the prepared pans. Cover and let rise for 45 minutes.
Preheat the oven to 400 degrees F.
Bake the loaves until golden brown on top and cooked through, 30 to 35 minutes. Remove to a rack to cool.