Muffins get a bad rap. Paraphrasing a British expression about US GIs – used disparagingly during WW2 – they are over-filled, over-sweet and over here. But muffins don’t have to be the gummy-textured, American-style behemoths beloved of overpriced (and over here) coffee chains. They don’t even need to be sweet. And, dear Lord, they can even be …