In a bowl, mix together the white and wholemeal flours. Add the salt, sugar and yeast and mix again until well combined.
Make a well in the centre of the dry ingredients. Gradually pour the warm water into the centre, bringing the dry ingredients into the pool of water using a fork. Keep stirring until the mixture comes together as a dough. You may not need to use all of the water - try not to allow the dough to become too sticky.
Turn the dough out onto a lightly floured work surface and knead well until smooth and elastic, for about 10 minutes.
Divide the dough into three equal-sized pieces and roll each into a ball. Knead one type of filling into each of the dough balls, so that each dough ball will be a different flavour and the flavours are hidden. Then tear each ball in two to make six buns in total.
Arrange the buns onto a lightly greased baking tray so that they are almost touching. Put the baking tray into a cold oven, then switch on the oven to 230C/450F/Gas 8 and bake the buns for 15-20 minutes, or until they have risen and are golden-brown. Set aside to cool on a wire rack.