In a microwave safe bowl, heat water for 30 seconds. Add melted butter and cold buttermilk. Pour all into a large mixing bowl, adding sugar, salt and yeast. Stir to blend. Add flour and mix until it forms a ball and fully incorporated. Cover bowl with a damp hand towel and let rise for about two hours in a cold oven, leaving the light on.
Remove bowl from oven. Dough should be about double in size. Stir to deflate.
Preheat oven to 375 degrees F.
Prepare a loaf pan with cooking spray. Pour dough into pan, cover again with a damp towel and allow to rest and rise for about 30 minutes.
Remove towel, and use a sharp knife to slice a line down the center of the loaf. Bake for 40-45 minutes or until golden brown.
Remove from oven and brush top with more melted butter. Let cool completely. Remove from pan and slice as desired. Tightly wrap with plastic to preserve freshness.