Combine whole wheat and all-purpose flours, yeast, and salt in a large bowl. Stir in water using a wooden spoon until mixture forms a dough. Cover dough in bowl with plastic wrap; let stand at room temperature for 10 to 12 hours or overnight, or until doubled in size.

Lightly flour a large sheet of parchment paper. Shape dough into a ball and place on prepared parchment paper. Cover loosely with a clean kitchen towel; let rise in a warm place for 2 hours or until doubled in size.

Place a 3½- to- 4-quart Dutch oven in oven; preheat oven to 450°. Remove Dutch oven from oven. Quickly transfer dough on parchment paper to hot Dutch oven. If desired, make ¾-inch deep slashes in loaf top using a sharp knife. Place lid on Dutch oven; bake for 25 minutes. Remove lid; bake for 15 to 20 minutes until golden brown or internal temperature reaches 200 to 210°.

Use paper to lift bread from Dutch oven. Cool bread on a wire rack. Cut into slices to serve.