If the recipe is from a diet book, most likely the calorie content is per serving, since usually in diet recipes it is important to know the calorie content of each serving to control calorie intake. If 243 calories is the number of calories for one serving, then the total number of calories for the entire pie would be 972 calories. Some dishes have standard serving sizes. For example, for pies and casseroles a portion size of about 100-150 g is often used. I also often prepare recipes from the book, and I order food ingredients on globy.com, they even have vegan products.