Melt butter in a large saucepan over medium heat. Add onion; cook 8 minutes or until tender, stirring frequently. Add garlic; cook 30 seconds, stirring constantly. Stir in broth, potato, salt, and bay leaf; bring to a boil. Cover, reduce heat, and simmer 15 minutes or until potato is tender.

Stir in kale and basil. Cover and simmer 10 minutes or until kale is tender. Discard bay leaf. Partially mash potatoes with a potato masher until thick and chunky. Top with cheese.

Combine first 5 ingredients in a large bowl, stirring with a whisk. Add yeast, stirring with a whisk; let stand 5 minutes. Lightly spoon flour into dry measuring cups; level with a knife. Add 2 cups flour to yeast mixture, stirring with a whisk. Cover and let rise in a warm place (85°), free from drafts, 15 minutes.

Add 2 1/2 cups flour, walnuts, rosemary, and 1 egg, stirring with a whisk. Turn dough out onto a lightly floured surface. Knead until smooth and elastic (about 10 minutes), adding enough of remaining flour, 1/4 cup at a time, to prevent dough from sticking to hands.

Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in size. (Lightly press two fingers into dough. If indentation remains, the dough has risen enough.)

Preheat oven to 400°.

Punch dough down; turn dough out onto a lightly floured surface. Divide dough in half, shaping each portion into a round. Place loaves on a baking sheet dusted with cornmeal. Cover and let rise 30 minutes or until doubled in size.

Combine 1 tablespoon milk and 1 egg, stirring with a whisk; brush over loaves. Make 3 diagonal cuts 1/4-inch deep across top of each loaf using a sharp knife.

Place loaves in oven; reduce oven temperature to 375°, and bake 40 minutes or until bottom of each loaf sounds hollow when tapped. Let stand 20 minutes before slicing.