To make the dough: Weigh your flour; or measure it by gently spooning it into a cup, then sweeping off any excess. Combine all of the ingredients in a medium bowl or the bowl of a stand mixer. , Mix until there are no dry spots; a plastic bowl scraper is your best tool if you're mixing by hand. Using a stand mixer, mix at low speed until all of the flour is moistened. The texture of the dough will be soft and sticky due to the pumpernickel flour. , Cover the bowl and let the dough rise at room temperature for 2 hours. Then refrigerate overnight, or for up to 48 hours., To bake bread: Grease your hands, and scoop the dough out onto a lightly greased or floured work surface. Shape it into a ball and place it, smooth side down, in a floured brotform; or in a bowl lined with a floured smooth cotton dish towel. Cover the dough and let it rise until it's very puffy, about 2 to 3 hours., About 45 minutes before the end of the rising time, start preheating the oven to 450°F with a 4- to 4 1/2-quart baking pot or casserole with a lid inside. Note: Make sure the manufacturer's directions for the baking pot or casserole you use say it's OK to preheat both the empty pot and lid in the oven before using. , When the loaf is fully risen, remove the hot casserole from the oven, carefully grease it, and tip the risen ball of dough into it. Make several slashes in the dough. Cover the pot with the lid, and place it on a middle rack in the oven., Bake the bread for 25 minutes. Remove the lid and bake for an additional 5 to 10 minutes; the loaf should be lightly browned, and the interior should register at least 195°F on a digital thermometer., Remove the bread from the oven and turn it out of the crock onto a rack. Cool for several hours before slicing.