Fastest Indy solve of the year so far for me, 13 mins. Unusually got many answers first from the definitions. Some excellent clues as always from Dac.
* = anagram
ACROSS
1 KIRS CH (irks)* church leaders = 1st 2 letters. It’s a brandy.
4 Robert BROWNING Excellent surface.
10 NO M (I N) ATES ref Billy no mates.
12 A-STREAM (as a term)* Favourite clue – a great &lit “Pupils likely to achieve highly as a term develops”
14 C LEAR SIGHTED “Cited”
17 DEMONSTRATOR Though it looks like there’s some wordplay, it’s a double definition.
20 DELI BES(t) (idle)* George Best ref musical score i.e. a composer. ‘briefly’ means ‘omit last letter’
22 TAG LINE (e.g. Latin)*
23 LINDA Cunningly hidden – indicated by ‘clothes’
DOWN
1 KEN DAL(e)
3 CANN(EL)LINI BEANS El = the Spanish in (nine cannibals)*
6 WAITING FOR GO (DO) T Samuel Beckett play do = party forgot = neglected circulate = go outside in container and contents
9 S (society) T (A MP) ACT Not sure if the surface is in line with the history of that tax in America.
15 STAR T OUT Another top drawer clue.
17 (D)ID(D)LER “Cheat and wastrel having hat encrusted with diamonds”. A little elaborate, this. I think it means the wastrel = idler has a hat of diamonds (D, from cards) – this is a down clue and also a second D included i.e. encrusted. Definition = cheat
(Testy’s note in comment 1 below explains this correctly, I’d say)
18 PI G OUT Pi = very good (from pious) Taste at Maxim’s = taste in French = gout.
21 SUPPE pp for it in suite 19th century composer.
I think I interpret 17 slightly differently. “I” is the “hat” for the word IDLER (i.e. the top when written downwards) so encrusting it with Ds for diamonds gives (D)I(D)DLER.
I was making excellent progress until the ‘new’ in 17ac convinced me that there was at least a partial anagram to solve, swiftly followed by a pencilled in FIRST for the first word in 15d, and I got a bit stuck. By the time I’d got DEMONSTRATOR, lunchtime had come and gone…
KENDAL (1D)
This seems to be as explained by nmsindy. But if so, it seems a bit odd: “…overlooking valley appears endless” arguably doesn’t give DALe, for the grammar is wrong for that: “valley” is the object in “Range overlooking valley” and the subject in “valley appears endless”. And why didn’t Dac simply say “Range overlooking endless valley …”? I suspect I’m missing something.