Fatty foods are often more flavorful because many flavors dissolve in fats. Butter works very well as a flavor carrier for spices, vanilla and other fat soluble ingredients. When you sauté an onion in butter before adding the base ingredients, all the flavor from the onions will be carried by the butter into the dish. Butter can be used to provide the primary, characteristic flavor of a sauce, as in Bechamel-type sauces, or in dessert toppings, such as butterscotch. The actual flavor we perceive once the food is in our mouths results from a combination of taste and smell to add flavor. The actual perception of tasting works like this: Our taste buds sense taste particles in food. The neurons associated with these cells send their taste messages to the brain. When food is placed on the tongue, smell particles travel to the olfactory neurons through the "back way" called the nasal pharynx which connects the mouth and the inside of the nose. Aromatic chemicals from the food (outside the mouth) go by the retronasal route by way of inhaled air to the olfactory neurons. These neurons have cilia that carry receptors for odor molecules. The molecules then bind to their receptors and messages are sent along these neurons to the olfactory bulbs at the base of the brain and then to various other parts of the brain for identification.
Butterfat is also inherently tasty. We are genetically programmed to seek out high-energy foods. There are at least five tastes: salty, sour, sweet, bitter, and umami. The umami taste is that of monosodium glutamate and has recently been recognized as a unique taste, as it cannot be elicited by any combination of the other four taste types. Glutamate is present in a variety of protein-rich foods, and particularly abundant in aged cheese. Recently, scientists have found that we can taste fat also, though the actual receptors are yet undiscovered.