-flour Will have a more or less sour taste, depending whether it is made with beer, buttermilk, potato water, or milk, in that order. Heat 1.5 cups liquid to lukewarm. Stir in the butter and salt. Set aside to cool. Dissolve the yeast in the warm water (a temperature comfortable on the inside of the wrist) with the sugar. Let stand for 5 minutes or until the yeast bubbles. Stir the yeast mixture into the cooled liquid. Add the rye flour and beat until smooth. Add the white flour, a cup at a time, stirring after each addition until enough is added to make a stiff dough. Dust a work surface with white flour. Form the dough into a rough ball, place it on the work surface, cover it with a damp cloth, and let it rest for 15 minutes. Generously butter a large bowl or pot. Adding only as much flour as necessary to prevent sticking, knead the bread dough until smooth, about 5 minutes. (The gluten in rye is more fragile than in wheat. It needs a resting time to recuperate and reform and does not need as lengthy or vigorous a kneading). Form the dough into a smooth ball and place it in a buttered bowl, turning it to coat all sides with the butter. Cover it and let it rise in a warm spot until doubled in size, about 2 hours. Punch the dough down, gently knead it for one minute, and divide it into two parts. Form each half into a round loaf and place the loaves in two lightly buttered 23 cm round cake pans or on a large, buttered baking sheet. Press a hole through the center of each loaf to give it a traditional shape if you wish. Cover and let rise until almost doubled in size, about half hour. Preheat the oven to 375 degrees. BRush the loaves with water and gently puncture the surface all over with the tines of a fork, in a design if you wish. Bake for about 30 minutes or until the bread is golden brown and sounds hollow when tapped on the bottom. While it is hot, brush it with butter to glaze, and then let it cool on a rack. Yields 2 round loaves.