I just mix 1 tbspn wheatbran, 2 tbspn oatbran, 1 tbspn sugar, then add water - 3 or 4 tbspn then put mix in a silicon sponge 'tin' and bake for about 15 or 20 mins.
For savoury omit the ugar and add pepper. for sweet add 1 tspn of reuced fat cocoa or 1/2 tspn ginger or some kind of spice - allspice or mixed spice or something.
the less water you add the thicker your biscuit will be. If you make it runnier it will spread out a bit more and be bigger. Also make smaller ones in a muffin tin.