APAD: Bob is your uncle

"Bob's your uncle" is a British English idiom meaning "and there you have it," "it's done," or that something is easy to achieve, used to conclude simple instructions or signify a successful, effortless outcome. Popularized in the UK and Commonwealth countries, it's similar to the French "et voilà!" and often follows a set of simple steps, like "Add flour, eggs, and milk, and Bob's your uncle, you have a cake!". 

The origin of the idiom is debatable  

One is Nepotism theory: A popular, though likely incorrect, story links it to Prime Minister Robert "Bob" Cecil (Lord Salisbury) appointing his nephew, Arthur Balfour, to a high-profile job in 1887, suggesting success came easily through family connections ("Bob's your uncle").  

Robert "Bob" Cecil

 

Some research suggests the phrase actually appeared in America first, used to mean something was quick and easy, and was later adopted and popularized by the British. 

Variation: 

Expressions of self-satisfaction or pride or delight at the end of a sentence describing an action, a situation, an instruction, or direction, especially when it seems easier or quicker than expected:

• A humorous or facetious gender-switching variant is "Roberta's your aunt" (or auntie).
• A long version is "Bob's your uncle and Fanny's your aunt". Versions sometimes spell your as yer.

Expressions with a stronger emphasis on easiness or delight:

• "Piece of cake", an informal expression for something very easy.
• "It's a dawdle", "it's a doddle"[5] and "it's a cinch",[6] other slang expressions for something very easy.
• "Easy peasy", a childish expression for something very easy.