In reply to:

is jewellery unique, then?

No it follows the same logic as one of your favourite words: travelling. Double to the "l" to add the suffix "ery".

travellery?? no, wait... ::slapping forehead with palm::
that's not what you meant...

gal >> gallery
distillery << distil

yeah, now I've got it!

>>a. Of the Eng. words ending in -ery many are adoptions from Fr., as battery, bravery, cutlery, nunnery, treachery. Many others are formed on ns. in -er, and are properly examples of the suffix -y; but in individual instances it is often uncertain whether a word was originally formed on an agent-noun in -er or directly on the verb. b. In modern, chiefly U.S., use, after bakery (= baker's shop or works), and similar words, this suffix has gained considerable currency in denoting ‘a place where an indicated article or service may be purchased or procured’, as beanery, bootery, boozery, breadery, cakery, carwashery, drillery, drinkery, eatery, hashery, lunchery, mendery, toggery, wiggery.

In many words this suffix has now the contracted form -ry, q.v.
-ry a reduced form of -ery, occurring chiefly after an unstressed syllable ending in d, t, l, n, or sh (the usual type being words of three syllables with the stress on the first), but also in a few cases after stressed vowels or diphthongs. The older examples sometimes represent OF. forms in -rie, with variants in -erie, but the great majority are comparatively late English formations. Examples of the various types are heraldry, husbandry, ribaldry, wizardry; casuistry, dentistry, harlotry, infantry, papistry, peasantry, tenantry; chivalry, devilry, rivalry; blazonry, yeomanry; Englishry, Irishry; avowry, Jewry. In some cases both -ery and -ry are in use, as baptist(e)ry, command(e)ry, jewel(le)ry.
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n.b. - once again we have an example of UK orthography with extra letters but the orthoepy then neglects them: "In commercial use commonly spelt jewellery; the form jewelry is more rhetorical and poetic, and unassociated with the jeweller. But the pronunciation with three syllables is usual even with the former spelling."

{latter quotes OED}