How to Make It
Lightly spoon whole wheat flour into dry measuring cups; level with a knife. Combine whole wheat flour, sugar, salt, and quick-rise yeast in a large bowl, stirring well with a whisk.
Combine milk, 1/2 cup water, butter, and canola oil in a microwave-safe bowl; microwave at HIGH 2 minutes, stirring every 30 seconds until mixture is warm (100° to 110°). Add milk mixture to flour mixture; stir 1 minute. Add egg; stir 1 minute. Lightly spoon bread flour into dry measuring cups; level with a knife. Add bread flour to yeast mixture; stir until a soft dough forms. Turn mixture out onto a lightly floured surface; knead 2 minutes.
Place dough in a large bowl coated with cooking spray; lightly coat top of dough with cooking spray. Cover and refrigerate overnight.
Preheat oven to 375°.
Turn dough out onto a lightly floured work surface, and punch down. Divide dough into 16 equal portions; shape each portion into a ball. Working with one ball at a time (cover remaining dough to prevent drying), roll dough into a 5-inch circle. Place about 1 1/2 teaspoons chocolate in the center of circle. Roll up dough tightly, jelly-roll fashion; pinch seams to seal. Place buns, seam side down, on a baking sheet lightly coated with cooking spray. Tuck ends under; cover. Repeat procedure with remaining dough and chocolate.
Lightly coat dough with cooking spray; cover and let rise in a warm place (85°), free from drafts, 40 minutes or until doubled in size. Lightly brush tops of buns with egg white.
Bake at 375° for 17 minutes or until lightly browned. Cool on a wire rack.