Pour boiling water over oats in a large bowl; let soften, about 1 hour. Add molasses, butter, and yeast; mix well. Add flour, 1 cup at a time, mixing well after each addition until dough sticks together. Cover with a towel and let rise in a warm place until doubled in volume, about 1 hour.
Butter two 9x5-inch loaf pans.
Punch down dough and turn onto a lightly floured surface. Shape into 2 balls and let rest for 10 minutes. Form balls into loaves and place into the prepared pans. Cover loaves with a damp cloth and let rise until doubled in volume, about 30 minutes.
Preheat oven to 375 degrees F (190 degrees C).
Bake loaves in the preheated oven until tops are golden brown, about 40 minutes.