Honest-to-goodness is a warm, informal way — a little old-fashioned, more American than British — of saying something is real, not fake, and often simple and good in a homely way. You almost always put it before a noun. An honest-to-goodness farmer is a real farmer, not someone playing one on TV. Honest-to-goodness soup is the homemade kind, not from a can. It is a set phrase, like a mild promise that you mean it (“honest to goodness”). You do not build it fresh each time, and you do not use it as a stiff legal word for “honest.” It sounds like a grandparent talking, not like a textbook. A close, stronger cousin is honest-to-God; goodness here is probably a softer stand-in, though you do not need that history to use the phrase.