Step 1

To make the preferment and soaker, in a large bowl, stir the flour, buttermilk and yeast; this is the preferment. In a small bowl, combine the farro and beer; this is the soaker. Cover both with plastic wrap and refrigerate at least 12 hours or up to 24.

Step 2

To make the dough, to the bowl with the preferment, add the soaker, both flours, 1 tablespoon each flax seeds, sesame seeds and pumpkin seeds, the salt, yeast and water. Using a silicone spatula, mix until no dry, floury bits remain; the dough will be thick and dense; do not overmix. Cover and let rise at room temperature until just shy of doubled, 1½ to 1¾ hours.

Step 3

Mist a 9-by-5-inch loaf pan with cooking spray. Using a silicone spatula, scrape the dough into the pan. With a dampened hand, gently flatten the dough into an even layer, pushing it to the edges and into the corners. Sprinkle evenly with the remaining flax, sesame and pumpkin seeds. Using a dry hand, gently press them into the dough so they adhere. Cover with plastic wrap and let rise at room temperature until the dough rises slightly (it will not double) and has a slightly domed surface, about 40 minutes. Meanwhile, heat the oven to 400°F with a rack in the middle position.

Step 4

Bake until the bread is deeply browned, pulls away from the sides of the pan and the center reaches 200°F, 60 to 70 minutes. Immediately invert the loaf out of the pan onto a wire rack, then turn it upright. Cool completely before slicing.