1. Cookbook - volume of recipes. Company (CO), right (OK), reserve (BOOK).
5. Opus - work. Anagram (stirring) of SOUP.
9. Scent - perfume. Homophone of SENT for dispatched. I'm not sure how 'without note' works exactly as the homophone indicator but it's clear what's intended.
10. Theorem - rule in maths. This is not an anagram (gets more confused) of the 7 letter 'article' but article (THE), anagram (confused) of MORE.
11. Act - a drama may have more than one. A (A), court (CT).
12. Hindrance - obstacle. Deer (HIND), bolted (RAN), initial letters of (C)aused (E)xtreme.
13. Desert - double definition.
15. Pauper - person with no money. The Times (PAPER) including upper-class (U).
17. Spaghetti - pasta. Anagram (cooking) of PAST EIGHT.
19. Mac - coat. Mother (MA) getting cold (C).
20. Unicorn - mythical creature. A rag mag is full of corny Uni jokes. Loi was eventually easy given the 'U' from 17dn.
21. Nudge - reminder. Naked (NUDE) outside (G)ym.
22. Kale - cabbage. King (K), beer (ALE).
23. Colliery - mine. Sheepdog (COLLIE) with (R)ascalit(Y).
1. Custard - sauce. Is it a sauce, is it a cream (creme Anglais), is it good on apple crumble - you betcha! Anagram (to be blended) of SAT CURD.
2. Overt - obvious. Finished (OVER) before time (T).
3. Butcher's Hook - I think this qualifies as a cryptic double definition. Cockney rhyming game slang for 'look' and as used in a butcher's.
4. Often - frequently. Somewhat alo(OF TEN)tative.
6. Parsnip - root vegetable. Standard (PAR), cut (SNIP).
7. Somme - river of north-eastern France. Millions (M) in a little (SOME).
8. Recreational - for enjoyment. Genuine (REAL) around the universe (CREATION).
14. Spaniel - breed of dog. Cross (SPAN), that is (I.E.), large (L).
16. Rockery - garden. China - not the first c(ROCKERY).
17. Skunk - American mammal. Doomed (SUNK) outside (K)ansas. A checking 'K' at the end of the word confused me into thinking this was from (K)ansas. Only when I put a K inside the answer did it become clear - opening the way to get unicorn.
18. Tango - dance. Beat (TAN), vitality (GO - as in get up and).
19. Midge - insect. For example (E.G.), slow witted (DIM) all rising.