Step 1In a large bowl, pour the boiling water over the mixed seeds. Set aside for 15 minutes to soften the seeds.
Step 2To the bowl, add the molasses, salt, buttermilk, beer and yeast. Stir to combine. Stir in the rye flour completely to form a smooth, runny dough. Cover the bowl with a towel or plastic wrap and set aside until puffed, bubbly and doubled in volume, about 1 hour depending on the temperature of the kitchen.
Step 3Slowly stir in the all-purpose and whole-wheat flour, and continue stirring until thoroughly combined to form a loose dough. Cover the bowl loosely with plastic wrap and place in the refrigerator to rise overnight.
Step 4Remove the dough and divide it evenly between 2 buttered 9-by-5-inch baking pans. The dough will still be very soft and will need to be spooned into the pans. Gently smooth the top of the dough. (It will be very sticky, do this the best you can.)
Step 5Loosely cover the pans with a towel or plastic wrap, and set aside in a warm place until doubled, about 2 to 3 hours depending on the temperature of the kitchen).
Step 6Heat the oven to 400 degrees. When the dough is doubled, prick the dough: Dip a chopstick or skewer into water and prick holes across the surface of the dough, about 1 inch apart, making sure to prick all the way through the dough. Pour the melted butter evenly over the dough.
Step 7Bake the bread until the top is a rich, dark brown and a thermometer inserted reads 205 degrees, about 1 hour, 20 minutes. Check the bread at half-hour intervals; if it colors too deeply and you worry about it burning, reduce the temperature to 350 degrees.
Step 8Remove the loaves to a cooling rack. Gently invert the pans and remove the loaves from the pans. Wrap each loaf in a towel and cool on the rack overnight. The loaves should cool for at least 1 day before slicing. Store the loaves in a plastic bag, and slice thinly to serve.