I SN'T this exciting. Keeping Posted has been invited to a ''Magic Evening with Chef Paul Prudhomme'' from New Orleans who will be displaying his skills on April 9 at Bayou Catering - reputedly this town's only authentic Cajun and Creole cuisine centre. Bearded Prudhomme will, we are informed, ''showcase his Louisiana cuisine and teach you how to use his magic seasoning blends''. Which is just the recipe for those of us with major gaps in our culinary education. Lori Granito, purveyor of all things spicy 'n nice at Bayou, proudly tells us that the bearded Prudhomme is the culinary genius who invented a cooking method called ''blackening''. Forgive us if we may appear a bit churlish. But we know quite a few people who whenever they get behind a hot stove specialise in nothing but that.