The phrase first catch your hare refers to the first step that must be achieved when a project is undertaken.
This expression and its variants with fish and carp instead of hare each appeared in the early 19th century as a misquotation of the initial instruction in a recipe from The Art of Cookery, made Plain and Easy, first published in 1747, by the English cookery writer Hannah Glasse (1708-70). According to The British Library, this book “was a best seller for over a hundred years, and made Glasse one of the best-known cookery writers of the eighteenth century”.
The earliest instance of one of those phrases that I have found is from The Oxford University and City Herald (Oxfordshire) of 2nd July 1808:
One of the new cookery books, in giving directions for a particular kind of pudding, begins thus, Take your maid and send her for a peck of flour. This reminds us of Mrs. Glasse’s receipt for dressing a carp, “First catch your fish,” &c.
The earliest occurrence of first catch your hare that I have found is from The Tyne Mercury; or, Northumberland and Durham, and Cumberland Gazette (Newcastle upon Tyne, Northumberland) of 18th July 1815:
“First catch your hare,” says Mrs Glass [sic] in her well-known direction for dressing poor puss; but the State cooks, when they made their late visit to the Tower to look out apartments for Bonaparte, seem to have neglected this very necessary preliminary.
Finally, the earliest instance of first catch your carp is from the Morning Advertiser (London) of 11th February 1819:
The Madrid Gazette contains an official declaration on the part of the Spanish Government, of the rigorous measures that will hereafter be pursued towards all foreigners who may be taken in South America, fighting on the side of the Insurgents. This is something like the recipe of Mother Glasse for dressing carp:—“first catch your carp and then kill it”—The menace will have no effect whatever in thinning the ranks of the Independents.
However, none of those instructions appear in any of the editions of the cookery book written by Hannah Glasse; in fact, she did not use the verb catch followed by an animal name.
It is often said that first catch your hare is due to a misapprehension of the following initial instruction in the recipe titled To Roast a Hare:
Take your Hare when it is cas’d and make a Pudding
(Here, the verb case means: to remove the skin from an animal by making a single slit along the hind legs and removing it whole. Hannah Glasse used take your followed by an animal name in several other recipes: “Take your Turky” [sic], “Take your Pigeons” and “Take your Pheasant”.)
But, as Jennifer Stead and Priscilla Bain wrote in Introductory Essays to the facsimile of the first edition of The Art of Cookery published by Prospect Books, London, in 1995 under the title First Catch Your Hare:
There must have been some further reason for the comment gaining almost catchphrase status. […]
There is first a common source to the phrase in that series of proverbs that warn against anticipating an event such as, ‘Don’t count your chickens before they are hatched’.
These authors then quoted the medieval Latin treatise De legibus et consuetudinibus Angliae, traditionally attributed to the lawyer Henry of Bratton:
Et vulgariter dicetur quod primo oportet cervum capere, et postea cum captus fuerit illum excoriare
And the common folk say that you must first catch your stag and after it has been caught skin it
They added that, however:
While there may be a general category of old saws to which the phrase could be allocated, there is no one specific saying to be produced as folk-precedent. Yet it had certainly gained currency by the 1850s and, it could be said, ran and ran thereafter.
Jennifer Stead and Priscilla Bain mentioned the 1850s because the earliest instances of first catch your hare known to them dated from that decade. The sole occurrence of a variant that they knew of was first catch your carp, from a book published in 1845.
The most likely explanation is that those phrases simply originated in popular humour jestingly ascribing them to Hannah Glasse’s cookery book or to others. This seems to be confirmed by the following from The Spirit of the Farmers’ Museum, and Lay Preacher’s Gazette (Walpole, New Hampshire – 1801):
A Rhetorician in a recent treatise upon his art, after recounting some of the most common errours [sic] in elocution, proceeds “to avoid these inconveniences, you ought to have a clear, strong voice.” This, the monthly reviewers say, reminds them of a recipe in an old book on the art of cookery: “How to dress a dolphin, first catch a dolphin, &c.”