This classic New England bread gets its texture and flavor from cornmeal and molasses.
Line 2 baking sheets with parchment. Sprinkle with cornmeal and set aside.
Pour 2 cups milk in small saucepan and gradually stir in cornmeal. Place over medium- low heat and stir constantly until mixture thickens, about 3 minutes. Transfer to a small bowl and set aside to cool.
In another small saucepan, combine remaining 2 cups milk, salt, molasses, and butter. Place over medium heat and whisk until butter is melted.
Transfer milk-and-molasses mixture to an electric mixer and let stand until milk is lukewarm (110 degrees). Sprinkle yeast over it, stir, and let stand until yeast dissolves and is foamy on top, about 5 minutes.
Add cooled cornmeal mixture and 4 cups flour to yeast-and-molasses mixture. Using the dough hook, mix on medium speed to combine ingredients. Slowly add remaining 6 to 6 1/2 cups flour in 3 or 4 additions, until dough is smooth and elastic but not sticky, about 5 minutes (or knead by hand for about 15 minutes). If necessary, turn the dough out onto a floured surface and knead in remaining 1/2 cup flour to keep it from being too sticky.
Spray inside of large bowl with nonstick vegetable-oil spray. Place dough in bowl, cover, and let rise in a warm place until doubled in bulk, about 1 hour and 40 minutes.
Punch down dough, turn it onto a work surface, and cut into 3 pieces. Shape each into an oblong loaf. Place 2 loaves on a prepared baking sheet and 1 loaf on another. Cover and let rise, about 1 hour.
Heat oven to 350 degrees. Whisk egg yolk with 1 tablespoon water. Brush loaves with egg mixture and sprinkle with remaining 2 tablespoons cornmeal.
Place loaves in oven and bake for about 40 to 45 minutes, until loaves are hollow sounding when tapped on bottom. Let cool on a wire rack before slicing.