How to Make It
Stir together 1 cup of the whole-wheat flour, 1/2 cup of the bread flour, 1/4 teaspoon of the yeast, and 1 1/4 cups of the water in a medium bowl. Stir until smooth. Cover with plastic wrap, and let mixture stand at room temperature until bubbly, 14 to 24 hours. (This makes the sponge.)
Stir together remaining 4 cups bread flour and 1 cup whole-wheat flour; set aside. When the sponge is ready, combine remaining 1 cup warm water and 1 1/2 teaspoons yeast in the bowl of a stand mixer fitted with a dough hook. Stir with a wooden spoon until yeast is dissolved, about 15 seconds. Stir in sponge and honey. With mixer on low, gradually add flour mixture and salt, beating until incorporated, about 5 minutes.
Transfer dough to a lightly floured surface, and knead until smooth and elastic, about 5 minutes, adding up to 1/4 cup bread flour, as needed, if dough is very sticky. Transfer dough to a large lightly greased bowl, and cover with plastic wrap. Let stand at room temperature until doubled in size, 1 to 1 1/2 hours.
Place a pizza stone on middle rack of oven. Preheat oven to 450°F. Line 2 rimmed 18- x 13-inch baking sheets with parchment paper. Turn dough out onto a lightly floured surface. Divide dough into 12 pieces. Working with 1 dough piece at a time, pat into a 4-inch square. Fold right and left halves in to meet in the center. Fold top 1/3 of dough down to the middle, and press to seal. Continue folding and pressing top third of dough down to form a tight 3-inch-long cylindrical loaf. With palms flat on work surface, place tips of thumbs together. Press thumbs into loaf, and slide loaf away from you several times to form a taut 4-inch-long football shape. Roll top and sides of loaf (not bottom/seam side) in benne seeds; transfer, seam side down, to prepared baking sheet. Repeat with remaining dough pieces, placing loaves 2 inches apart. Let rise, uncovered, until almost doubled in size, 45 minutes to 1 hour.
Using a sharp, thin knife, cut a 3-inch-long (1/4-inch-deep) slit across the top of each loaf. Place 1 baking sheet on preheated pizza stone, and bake until golden brown, seeds are lightly toasted, and internal temperature registers 205°F, 18 to 22 minutes. Remove from oven, and repeat with remaining baking sheet. Serve loaves warm, or transfer to a cooling rack to cool completely, about 30 minutes.