Mashed Potato Bread

Preparation

1. Step 1

   Boil potato in 2 cups water in medium saucepan until very tender, about 15 minutes. Strain 1 1/2 cups cooking liquid into large bowl (add more water if needed to measure 1 1/2 cups). Cool liquid to 105°F to 115°F. Mash potato in small bowl until smooth. Add mashed potato and 1 teaspoon yeast to cooking liquid. Cover bowl with plastic and let starter stand at room temperature overnight.

   Step 2

   Pour 1/4 cup warm water into small bowl. Sprinkle remaining 1 teaspoon yeast over; stir to blend. Let stand until yeast dissolves, about 10 minutes. Stir yeast mixture into starter. Stir in melted butter, honey and salt. Mix in whole wheat flour. Mix in enough all purpose flour, 1/2 cup at a time, to form soft dough. Turn dough out onto floured work surface. Knead until smooth and elastic, about 4 minutes. Form dough into ball.

   Step 3

   Butter large bowl. Place dough in bowl; turn to coat. Cover with plastic. Let dough rise in warm draft-free area until doubled in volume, about 1 hour. Lightly flour 2 large baking sheets. Punch down dough. Turn dough out onto floured work surface and knead until smooth, about 3 minutes. Divide dough in half. Roll each half between palms and work surface into 14-inch-long loaf. Transfer to prepared baking sheets. Cover with dry towel. Let rise in warm draft-free area until almost doubled in volume, about 30 minutes.

   Step 4

   Position 1 rack in center and 1 rack in top third of oven and preheat to 500°F. Using sharp knife, cut 5 diagonal slashes in surface of each loaf. Brush loaves with egg white. Bake loaves 10 minutes. Reduce oven temperature to 400°F. Bake until loaves are brown and sound hollow when tapped on bottom, switching and rotating baking sheets halfway through baking, about 15 minutes longer. Cool on racks. (Can be prepared 2 weeks ahead. Cool completely. Wrap loaves separately in foil, seal in plastic bag and freeze. Thaw loaves, then rewarm, wrapped in foil, in 350°F oven 15 minutes.)