Activate Yeast: In a large bowl, combine ¾ cup warm water, 1 tsp sugar, and yeast. Let stand 5-7 mins until foamy.
Combine Dry Ingredients: In a separate bowl, whisk flours, flaxseed meal, baking soda, and salt.
Form Dough: Add dry mix and 2 tsp sugar to yeast. Begin by gradually mixing in about 1 cup of the warm water (or water/milk combo from the total 1 ½ cups). Continue to add more of the remaining water slowly, a little at a time, observing the dough's consistency, only adding enough until the dough starts to come together and looks shaggy but not overly wet (you may not need all 1 ½ cups). Add oil; mix until a smooth, slightly tacky dough forms. Add a bit more water if too dry.
Knead: Knead on a lightly floured surface or in a mixer with a dough hook for 6-8 minutes total, until smooth and elastic.
First Rise: Place dough in an oiled bowl, cover, and let rise in a warm spot for ~1.5 hours, or until doubled.
Shape Buns: Gently deflate dough. Divide into 12 equal pieces; shape into smooth balls.
Second Rise: Place on parchment-lined baking sheets, 2 inches apart. Cover; let rise in a warm spot for ~1 hour, or until puffy.
Preheat & Prep Topping: Preheat oven to 375°F (190°C). Mix topping ingredients if using.
Bake: Brush buns with optional topping and sprinkle with seeds. Bake 22-27 minutes, until golden.
Cool: Transfer to a wire rack to cool completely.