When I was a kid, my mom made Martha White bran muffins all the time. In the olden days, the mix came in a small paper bag, so she could just tear off the top, stir in some eggs, and have the muffins baked off by the time my brother and I got up for school. We'd split 'em open and just pile on the butter, neutralizing whatever health benefit they might have offered.
Funny thing is, it's nigh impossible to find a decent bran muffin recipe online. Most start with an entire box of bran flake cereal, which seems like a rather convoluted way to incorporate whole grains into the batter. Besides, with my limited pantry space, I'd rather stock a small bag of wheat bran that can produce ten batches of muffins than be forced to deal with that many boxes of cereal.
The thing about wheat bran is that you can't just sprinkle some into your muffin batter; the dry flakes are so incredibly absorbent that even an ounce or two is enough to suck up every last drop of moisture from the entire batch. Without access to that water, the gluten-forming proteins in the flour can't interlink, which weakens the structure of the batter, leading to fragile muffins that crumble apart at the touch.
Heat helps the flakes hydrate a little faster, but it can also melt the butter in the batter, turning it soupy and thin. Thin batters tend to bake up flat, which is great for a nice and level cake but sad when it comes to a muffin. To keep the batter thick, for muffins with a nice round dome, the hot bran mash needs to be cooled to room temperature. You could do that passively by just waiting around, or instantly by stirring in cold yogurt and eggs.
I like using Greek yogurt because it's strained, which keeps the batter nice and stiff, ensuring that each muffin bakes up with a beautiful crown. Since the bran mash is already loaded with water, trading Greek yogurt for milk, buttermilk, or even plain yogurt would only thin the batter, leading us back to those sad, flat-topped muffins.