Boule is the French term for a large round loaf of bread thats often made with sourdough. Here, buttermilk gives the loaf the same kind of tang without having to use a sourdough starter.
Stir yeast into 1/2 cup warm (110F) water, and let stand 5 minutes, or until liquid is cloudy and bubbles begin to form on surface. Combine buttermilk and honey in small heatproof bowl. Microwave on high 30 seconds, or until warm to the touch. Whisk yeast mixture into buttermilk mixture with fork.
Combine flour and salt in large bowl. Stir in buttermilk mixture until thick dough forms. Transfer dough to well-floured work surface, and knead 7 minutes, or until dough is elastic and no longer sticks to your hands. Form into ball, and set in lightly oiled bowl. Cover with clean dish towel, and let rise 1 hour in warm place.
Punch down dough, and gather into tight, smooth ball. Coat baking sheet with cooking spray; place dough on it. Cover again with dish towel, and let rise 40 minutes in warm place.
Preheat oven to 375F. Cut diagonal slashes across top of loaf with sharp knife. Bake 35 to 40 minutes, or until golden brown. Cool, slice and serve.