Disfunctional Muffins!

Can anyone share with me a fool-proof recipe for mountainous American-style muffins ('big fairy cakes' :-)? Every recipe that I've tried - 'Joy of Cooking', "Laurel's Kitchen Bread Book", Mary Berry - has turned out blueberry fairy cakes instead... I suspect my baking powder, in that I can't find 'double-acting' in the UK?