Preheat oven to 375°. Lightly butter an 8×4” loaf pan and line with parchment paper, leaving generous overhang. Place yeast in a medium bowl (or the bowl of a stand mixer) and add 1 cup warm water; stir to dissolve yeast. Add cornmeal, molasses, hemp seeds, nigella seeds, golden and brown flaxseed, poppy seeds, salt, 2 cups flour, and 2 Tbsp. unsalted butter. Using a wooden spoon (or dough hook if using stand mixer), mix until no dry spots remain.