The expression baking hot is used of excessive heat. In this expression, the adverb baking is an intensifier.
This expression occurs, for example, in World news in brief, published in The Independent (London, England) of Wednesday 16th March 2022 [page 28]:
Scientists are already virtually certain that 2022 will be among the 10 hottest years on record. In its monthly update, the National Oceanic and Atmospheric Administration, a US federal agency, reported that this year was already off to a baking-hot start.
The earliest occurrences of the expression baking hot that I have found are as follows, in chronological order:
1-: From Liverpool (Aintree) Meeting, dated Liverpool, Saturday 6th July 1833, by Alfred Highflyer, published in The Sporting Magazine, or Monthly Calendar of the Transactions of the Turf, the Chase, and every other Diversion, interesting to the Man of Pleasure, Enterprise & Spirit (London, England) of August 1833 [Vol. 7, 2nd Series, No. 40, page 324, column 1]:
Thursday—Blooming, baking-hot weather, and a good muster.
2-: From Dr. Maginn. A Literary Retrospect by a Middle-Aged Man, by the English author Katherine Thomson (née Byerley – 1797-1862), published in Bentley’s Miscellany (London, England) in 1845 [Vol. 18, page 589]:
How is it that in this great metropolis there are no good lodgings to be had? […] In winter a tea-spoonful of coal in your fire-place; in summer a baking hot atmosphere; no ventilation, no good cleanings to refresh the apartments; suffocating nights and days.
3-: From a letter by the English preacher and author Joseph Barker (1806-1875), in Objections to a Steam Press, published in The Christian (London, England) in 1846 [Vol. 2, No. 29, page 109]:
Do they get ovens and grates that take double the quantity of coal and yield only half the proper quantity of heat, when they can get ovens and grates that will give the necessary amount of heat with half the coal? Do they not like to make their pots boil, and their ovens baking hot, at as little expense of coal, and with as little trouble as possible?
4-: From The Pleasures of Entomology, by the Editor, published in The Entomologist’s Annual for 1856 (London: John Van Voorst, 1856) [page 6]:
The pleasures of the collector of insects, even of the mere collector, are of a high order—compare them with the pleasures of the collector of coins, or the collector of autographs, &c.; the collector of insects, however he may enrich his collection by specimens received from others, will still make the larger part of his collection himself; most of the specimens will be his own captures, and the sight of them will remind him of the place of capture: the sloping down, with its short, slippery turf; the country lane, with its tangled hedges, where honeysuckle and bramble help to bind in friendly harmony the hazel, the dogwood and the oak; the sandy heath, where it was so baking hot in the sun, but where at evening the purple heather was perfectly swarming with moths.
5-: From Stenolophus elegans: a History, by J. W. Douglas, published in The Entomologist’s Weekly Intelligencer (London, England) of Saturday 18th July 1857 [Vol. 2, No. 42, page 126, column 2]:
On the 28th of June—a baking hot day—I went on an exploring mission to Sheerness [&c.].
6-: From Stenophilus [sic] elegans: a History, by J. W. Douglas, published in The Zoologist: A Popular Miscellany of Natural History (London: John Van Voorst, 1857) [Vol. 15, page 5,786]:
On the 28th of June, a baking hot day, I went on an exploring mission to Sheerness [&c.].
7-: From Suggestions respecting Tineina for a Traveller in South America, by H. T. S., published in The Entomologist’s Weekly Intelligencer (London, England) of Saturday 22nd May 1858 [Vol. 4, No. 86, page 64, column 1]:
Family VI. Glyphipterygidæ.
How luxurious it would be on a baking hot day to sit down in the shade and watch an insect twice the size of Thrasonella, and all pearl and gold, fan itself!
8-: From Female Influence (London: Hurst and Blackett, 1859), by the English author Charlotte-Maria Pepys (1822-1889) [Vol. 2, page 122]:
Everything seemed very disagreeable; there was a cold wind, and the sun was baking hot, the flies were troublesome.
9-: From Australian Facts and Prospects: To which is prefixed the author’s Australian autobiography (London: Smith, Elder and Co., 1859), by the English author Richard Hengist Horne (Richard Henry Horne – 1802-1884) [page 175]:
The Australian man of progress […] is certainly changing the temperature of the land of his adoption, so far as relates to its objectionable effects. […] The mean annual temperature remains, with only a slight variation, but the injurious effects are disappearing. These changes were becoming apparent two years ago, and they are not likely to be stopped now, even by the occasional presence of a few baking hot days, extensive bushfires, or even another Black Thursday *.
* On ‘Black Thursday’, i.e., 6th February 1851, European settlers in Victoria, Australia, faced their first catastrophic bushfires, which burnt a quarter of the colony.
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