1. Preheat the oven to 350ºF (180ºC). On one baking sheet, spread the sunflower seeds, oats and wheat germ in separate rows. On another baking sheet, spread the millet, sesame seeds and flax seeds in rows. Toast the contents of both baking sheets in the oven until the seeds are lightly browned, about 6 minutes. (If they start getting too dark on top, give them a gentle stir, while keeping the seeds, oats, and germ in their own lanes.) Cool to room temperature.
2. To the bowl of a food processor, add the sunflower seeds, wheat germ, all-purpose and whole-wheat flours, baking powder, baking soda, and salt. Process until the mixture is pulverized. Add the oats, millet, sesame and flax seeds, and poppy seeds to the bowl of the food processor and pulse a couple more times, just enough to combine everything, but no further.
3. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter until light and fluffy, 2 to 3 minutes. (You can also make it in a mixing bowl and use a sturdy spoon or spatula to mix the batter.) Add the sugar and continue to beat until the mixture is smooth and creamy. Add one egg and beat in well, stopping the mixer to scrape down the sides of the mixer bowl, so the egg gets fully incorporated. Add the second egg, and mix (and stopping and scraping the sides of the bowl), until the second egg is combined.
4. On low speed, mix in the honey, then the buttermilk. Stop the mixer (I like to do this step by hand, but you can do it in the mixer), gently stir the flour and seed mixture into the butter and eggs in three additions, making sure that you don’t overbeat the batter.
5. Line a 12-cup (or two 6-cup) muffin pan(s) with paper baking cups, or butter the indentation. Mix the four seeds in the 4-seed topping together in a small bowl. Sprinkle 1/2 teaspoon of the seed mixture into each baking cup.
6. Fill each muffin cup right up to the brim with the muffin batter. You can use a spring-loaded ice cream scoop, two soup spoons, or a pastry bag fitted with a large, plain tip. Level the tops of the muffins with a small spatula or spoon. Sprinkle 1 teaspoon of the 4-seed mixture over the top of each muffin and bake until the muffins feel just cooked in the center, about 25 minutes.