These little cakes are one of my favorite desserts for company.  They're so surprising- the light, almost souffle like cake rests atop a silky smooth sauce at the bottom like a layer of pudding or curd.  They are bright and tart, a perfect use for the winter citrus and just the right sort of pick me up on grey days.  The cakes can be made in ramekins for individual servings or in a single baking dish to serve family style.  One tip: don't skip the step where you rub the lemon zest into the sugar.  It really is the key to getting as much lemon flavor as possible into the cake.