I think the theory is that the eggs act as raising agent, so if you miss out the baking powder, you may need more egg.
My recipe is similar to Chris, but I use less eggs and I do add 1/2 teaspoon baking powder. It makes 6 muffins, sweet or savory and I find 2 muffins a day is just fine for me. Freezes well so I batch cook when I feel like it.
4 tablespoons oatbran
2 tablespoons wheatbran (can subsitute oatbran if not taking wheatbran)
2 eggs, separated
1/2 a tub of Quark (or Fromage frais)
1/2 teaspoon of baking powder
generous pinch of salt
For sweet muffins, I also add 2 tablespoons of sweetener ( I use Xylitol but whatever you use is fine and some people prefer none)
I first beat up the egg whites till theyre stiff. Then I put all the dry ingedients in a big bowl, and add the egg yolks and the quark. I also add herbs or spices or whatever flavours I'm using, and mix well. The quark I prefer comes in 250g tubs, and I find half a tub does a 6 muffin mixture, but you could use fromage frais instead. It may make it a slightly wetter mix, so probably best to use less.
Then I gently fold in the egg whites to the big bowl mixture, and add in any chopped chunks of fish/meat or goji berries so it gets well dispersed. Then pop into 6 cup silicone mould, into hot oven (around 180-200 C) and bake for about 20 mins. You can tell theyre done from colour and also they are firmer in the middle - I have to turn mine around at 15 mins because oven is a bit temperamental.
Savoury flavours Ive done are-
chicken & chilli
ham & herbs
crab & smoked salmon
fennel seed & smoked salmon
prawns & herbs
cumin seeds & chicken
Sweet include -
orange/lemon zest & spices
low fat cocoa powder (2 tablespoons I find is OK)
Vanilla essence
Coffee
Goji berries (2 tablespoons ish)
lavender
fresh ginger
Spices - I use cinnamon a lot, also allspice, mixed spice etc, I find 2 teaspoons is usually enough for me
I've not tried many of the Dukan flavourings in the muffin mixes (I like them in yoghurt) but I did try the pistachio and that was OK, and I've also used a non Dukan orange essence flavouring.
Its good fun experimenting! And as my OH said, he'd eat these even if he wasn't dieting!