Llaisdy

Masterpieces from cooks badly overdue (5-7)

masterpieces (from)
"cooks"         : "chefs", synonym of "cooks"
badly "overdue" : jumble letters of "overdue" => "doeuvre"
=> "chefsdoeuvre"

Cook once stuffing spring chickens in here (3,4)

cook "once" : jumble letters of "once"    => "enco"
stuffing    : insert previous into following
"spring"    : "hop", synonym of "spring"  => "h enco op"
-: chickens in here
=> "hencoop"

Hot Finnish sauna ultimately designed to inspire love (2,7)

hot :-
"finnish"          :                             => "finnish"
"sauna" ultimately : last letter of "sauna"      => "s"
designed           : jumble previous             => "infashin"
to inspire         : insert following into previous
"love"             : "o"  # 0, synonym of "love" => "infashi o n"
=> "infashion"

As the programming language and the data to be processed are both English, much of the challenge is deciding which words are data and which code.

A word can represent an instruction (a transformation or function), itself (“raw data”) or a synonym of itself (a zero-argument function). Synonyms do not respect part of speech.

Any word can play any role in any clue. “Hot” is a good candidate for a jumble instruction; “cook” often stands for itself or its synonyms (e.g. “chef”).

(All clues are from recent FT crosswords.)