No. Casta sauce is a kind of dessert sauce, which is mainly made of milk, sugar, egg yolk and low-gluten flour. It tastes delicate, sweet and delicious. Margarine, on the other hand, is made of hydrogenated vegetable oil, which is usually used as a low-fat and low-sugar substitute. Casta sauce and margarine are very different in composition. Therefore, custard sauce is not margarine.