Bob's your uncle

Example: “Add the water, stir for a minute, and Bob's your uncle: pancake batter.”

Origin: The story everyone tells involves Robert Gascoyne-Cecil, Lord Salisbury, who as prime minister appointed his nephew Arthur Balfour to the sensitive post of Chief Secretary for Ireland in 1887 — an act of nepotism blatant enough that a phrase meaning "and there you have it, effortlessly" would be a fitting sarcastic monument to it, with Bob standing in for Robert. The problem is the gap. The expression is not attested until the 1920s, roughly four decades after the appointment, and forty years of complete silence is difficult to explain for a phrase supposedly coined as a topical joke. Etymologists therefore treat the Salisbury story as unproven, and some suspect the phrase is simply a nonsense tag of the kind English generates freely, with the Balfour explanation attached later because it makes such a satisfying story.