How to Make It
In a large bowl, whisk both of the flours with the cracked rye and the flax, sunflower and sesame seeds.
In the bowl of a stand mixer fitted with the dough hook, mix the water with the buttermilk, beer, salt and yeast at low speed until combined. Add the dry ingredients and mix at medium-low speed until incorporated and the dough is the consistency of a thick cake batter, about 10 minutes.
Lightly grease two 9-by-4-inch loaf pans and divide the dough between the pans; smooth the top of the dough with a spatula. Each loaf pan will have about 2 1/2 pounds of dough. Cover loosely with plastic wrap and refrigerate overnight, at least 12 hours or up to 6 days.
Remove the loaf pans from the refrigerator and let stand at room temperature in a warm place until an instant-read thermometer inserted in the center of the dough reads 73°, about 3 hours. Preheat the oven to 350°. Unwrap the dough and bake for 2 hours, until the crust is a deep brown and an instant-read thermometer inserted in the center reads 200°.
Transfer the loaf pans to a wire rack and let cool for 30 minutes. Carefully remove the bread from the pans and let cool completely, about 2 hours.
Cracked rye can be found at some health food stores and on amazon.com.