Salt; and a mirepoix of onions, garlic, and ginger — slow cooked.
No but seriously.
Taste is obviously subjective — oh so subjective — making it difficult to delineate its essence. I suppose one could claim that quality is the essence of good taste. But what is quality? How does one determine good quality?
Perhaps the essence of good taste is experience. The more varieties of food you eat, or wine you drink, or music you listen to, or books you read, or fill-in-the-blank, the quality of your taste becomes more refined and thus, better.
Another way to think about it may relate to our awareness of our tastes. That is to say, their evolution and emergence. That means knowing why you have a taste for something. Remembering a time when your taste was different, and how it evolved into what it is now. While every person’s taste in everything, no matter what, is valid in their own right, it may not be good. If you’ve “always liked it this way” or “not sure why but prefer X over Z”, then it’s possible your taste isn’t ‘good’, since it may not have been the result of experience and determination, but rather a default position, superimposed by the diametric forces of culture.