Step 1
Mix rolled oats buttermilk and molasses in a large bowl until thoroughly combined.
Step 2
Whisk together whole wheat flour all-purpose flour salt baking soda and cream of tartar until combined; pour flour mixture into buttermilk mixture and stir just until moistened.
Step 3
Turn dough out onto a lightly-floured work surface and knead 3 or 4 times until dough holds its shape.
Step 4
Cut dough in half; pat each half into a 6-inch round loaf.
Step 5
Use a sharp knife to deeply score each loaf in quarters cutting 1-inch deep.
Step 6
Wrap each loaf in plastic wrap and allow to stand at least 12 hours at room temperature to ferment. (Loaves can be refrigerated up to 2 more days after this if desired.)
Step 7
Preheat oven to 400 degrees F (200 degrees C).
Step 8
Place loaves on an ungreased baking sheet.
Step 9
Bake loaves for 15 minutes and reduce heat to 350 degrees F (175 degrees C). Continue to bake until loaves are browned and make a hollow sound when tapped on the bottom about 20 more minutes.
Step 9
Allow breads to cool for 10 minutes before slicing. To serve slice loaves 3/4-inch thick all across the loaf then cut slices in half.