In British English, the noun crackling, which denotes the crisp skin or rind of roast pork, is used figuratively and colloquially of women regarded collectively as objects of sexual desire. And the phrase a bit, or a piece, of crackling is used of a woman regarded as an object of sexual desire.

—Cf. also the noun crumpet, used in British English to denote 1) women regarded collectively as objects of sexual desire; 2) sexual intercourse—and the phrase a bit, or a piece, of crumpet, denoting 1) a woman regarded as an object of sexual desire; 2) a sexual act.

Both the noun crumpet and the phrase a bit of crackling occurred in News flesh on the box, by Tom Brown, published in the Daily Record (Glasgow, Lanarkshire, Scotland) of Monday 11^th January 1993:

Here is a news flash: Fiona Armstrong crosses her legs, and reveals a portion of plump and pretty thigh.
Now, Fiona’s pins aren’t at all bad.
But, last week, they were bigger than the Shetland oil disaster, Bosnia AND the Royal troubles put together . . . in news terms, that is.
She’s been made over, glammed-up, given a paint job and had her hair—and skirts—shortened by her new bosses at GMTV.
[…]
Presenters MUST have the F-factor. (Wash your mind out, you at the back—this ‘F’ stands for fanciability).
Breakfast TV is now served up with crumpet and a nice bit of crackling.
The presenters aren’t there to keep you up to date with what’s happening in the world—they’re there to flirt.
[…]
TV these days is about the March of the Bimbos, while the more mature women presenters are quietly given their marching orders.
[…]
Why not go the whole hog? Why not topless girl news-readers—and weather forecasts by Page Three girls?

The first two occurrences that I have found of the phrase a bit (also a piece) of crackling used in the sense of a woman regarded as an object of sexual desire are as follows, in chronological order:

1-: From Pets of Aldershot, by “Trooper Tommy Atkins”, published in The Penny Illustrated Paper and Illustrated Times (London, England) of Saturday 28^th December 1895:

Tommy Atkins has a distinct partiality for all that appertains, even in the most remote degree, to the stage. As a man, he is, of course, fond of feasting his eyes on the numerous “lumps of loveliness” that display their charms before the footlights, and, in accordance with the traditions of his calling from time immemorial, he is generally the devoted admirer of some dozen or so divinities at the same time.
[…]
[…] In conversation, he will refer to these young ladies individually as “a tasty bit of skirt” or “a bit of orlright,” and in his more exuberant flights of fancy has even been known to speak of an exceptionally fascinating damsel—such as Pierrette—as a “spicy bit of crackling.”

TOMMY’S PIERRETTE.

2-: From The Era (London, England) of Saturday 23^rd October 1897—Marie Lloyd was the stage name of the British music-hall artiste Matilda Alice Victoria Wood (1870-1922):

MARIE LLOYD IN NEW YORK.
(FROM A SPECIAL CORRESPONDENT.)

Marie Lloyd was welcomed back to New York by a very large audience at Koster and Bial’s on Monday, the 11^th, and scored an immediate success. Her entrance was the signal for hearty and continuous applause, and it was evident that the audience regarded her as an old favourite. […] The barmaid was the subject of the next song. The different customers who pester her with attentions or make her the object of criticism were described by Miss Lloyd in mirth-provoking fashion. First the would-be masher, who “does the heavy,” and is killingly polite, but who, in spite of his pretentious air, is never good for anything more expensive than “bread and cheese and bitter.” Then the sporting gents., who dilate on her good “points,” compare her to a two-year-old, and, in the jargon of the turf, make other remarks of a would-be complimentary nature. The ladies are not so kind. They refer to her as “a forward bit of goods,” insinuate that her hair is dyed, and make other spiteful remarks. “The idol of the Rose and Crown” also has to stand the fire of coster criticism. The coster is accompanied by his “lady friend,” but that doesn’t prevent him from being smitten with the barmaid’s charms, and over his accustomed “pot of fourpenny” he dilates upon them in the expressive vernacular of his kind, referring to the object of his remarks as “a dry bit of crackling,” and making other choice comparisons.
The barmaid is not the familiar figure in New York that she is in London, but that did not prevent the audience from enjoying the rich humour of a faithful character sketch.

The phrase a bit (also a piece) of crackling then occurs in two songs:

1-: In a song performed in Aladdin, a pantomime produced at Brixton—but the meaning of the phrase cannot be inferred from the context:

1a-: As mentioned in The Morning Post (London, England) of Tuesday 27^th December 1898:

The house was tickled by the topical duet between Aladdin and the Widow Twanki, “A little bit of crackling on a fork,” and also by that between two policemen, “Capital and Labour.”

1b-: As mentioned in The Standard (London, England) of Tuesday 27^th December 1898:

Aladdin and the Widow Twanki join in an amusing topical duet with the lengthy title of “The tasty piece of crackling on the pork [sic].”

2-: In a song mentioned in the Windsor and Eton Express, Berks, Bucks, Surrey, and Middlesex Journal; Maidenhead and Slough Gazette (Windsor, Berkshire, England) of Saturday 22^nd March 1902—but the meaning of the phrase cannot be inferred from the context:

Concert at the Liberal Club.—A concert was given at the Liberal Club on Wednesday evening […]. The following were the items:—[…] comic song, “He called me his little bit of crackling,” Mr. Victor Travers.

The phrase a bit (also a piece) of crackling then occurs in the sense of a woman regarded as an object of sexual desire:

1-: In The Necessary Colour, by ‘Doss Chiderdoss’, published in The Sporting Times (London, England) of Saturday 3^rd August 1907:

As an anecdotist, too, he all at once gained favour rare,
And he quite amused the ladies with his cackling;
But it clearly was his aim to win the goodwill of the pair,
And especially one “little bit of crackling.”
’Twas to her he gave his choicest gems of anecdote and wheeze,
Some of which, no doubt, required the censor’s eyes on;
For ’twas only when she said to him, “No more of that sort, please!”
He remembered he’d his old blue tie on.

2-: From The Tees-Side Weekly Herald (Middlesbrough, Yorkshire, England) of Saturday 28^th September 1907:

The judge of the Middlesbrough County Court has recently had to deal with the questions whether a wife may help herself to an independence by appropriating the balance of money given to her by her husband for housekeeping without her husband’s consent, says a writer in “London Opinion.” The county court judge held that she could not, and the “Law Journal” says the decision is both good law and good sense. As a matter of law—and law is mostly based on sound social policy—the wife is for this purpose the agent of her husband—entrusted with money for a specific purpose, and accountable to the husband for the application of it. […]
[…] You know—you poor, dear, suffering women—how the wretches dole you out just sufficient to provide the bare necessities of life, and that all your cleverness is needed to make two ends meet, much more to pinch enough to buy yourself a new mantle or a summer toque. You are now pronounced to be an “agent.” “Agent,” indeed. He didn’t call you his “agent,” did he, when he used to wait for you in the lane and coax you to kiss him in the shrubbery—although you told him at the time that you would much rather not do it if you studied your own inclinations? No, you were his “own little bit of crackling” then, quite a multum in parvo, in fact, in the way of dainty comestibles.