Step 1

Whisk together bread flour, rye flour, whole-wheat flour, salt, and yeast in a large bowl. Stir together water and molasses in a medium bowl. Add to flour mixture; stir until flours are incorporated. (Dough will be very sticky.) Scrape dough into a large bowl coated with cooking spray. Cover and let rise in a warm (85°F) place free from drafts 3 hours.

Step 2

Scrape dough onto a floured surface. Fold dough into thirds, like folding a letter. Rotate dough 180°F. Repeat folding and rotating procedure 2 times. Coat an 18-inch piece of parchment paper with cooking spray. Place paper, cooking spray side up, in a large bowl. Place dough, seam side down, in prepared bowl. Cover and let rise in a warm (85°F) place free from drafts 30 minutes.

Step 3

Preheat oven to 450°F. Place a 4-quart Dutch oven in lower third of oven. (Do not remove Dutch oven while oven preheats.)

Step 4

Remove Dutch oven from oven. Carefully place dough on parchment in hot Dutch oven. Cover and bake in preheated oven 30 minutes.

Step 5

Uncover and bake until well browned and a thermometer inserted in center of bread reaches 195°F to 205°F, 5 to 10 minutes.

Step 6

Transfer bread to a wire rack, and cool completely, about 1 hour.