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In the following snowflake-shaped crossword puzzle, 44 words can be filled in by solving straightforward crossword clues (listed below). The remaining spaces are to be filled with words appearing in a (well known) mystery Christmas song whose (partial) lyrics are reproduced below the clue list, with unclued words replaced by 'BLANK'. Line breaks have been removed from the song excerpt to disguise it further.
TASK: Fully resolve the crossword puzzle, and deduce and name the associated Christmas song.
Across (A):
3. Fruit with a tough shell (3)
19. In good physical condition (3)
23. Faucet (3)
24. Sweet potato (3)
27. Hawaiian island (4)
36. Moose (3)
43. Adhesive (4)
44. Cap, for a jar (e.g.) (3)
46. Taxi (3)
48. Parabola (3)
59. Not closed (4)
60. Apiece (4)
61. Positive response (3)
Down & Left (DL):
5. Squall, or flurry (4)
11. Small, green vegetable (3)
13. Break, split (4)
14. Cereal plant (3)
23. Noise of displeasure? (3)
29. Unit of resistance (3)
31. Domesticated ox (3)
39. Ukrainian Gunner, Luzhny (4)
41. Sphere (3)
50. Belonging to him (3)
51. Fresh (3)
54. French cheese (4)
Down & Right (DR):
1. Pale (3)
4. Numbers between 12 and 20? (5)
9. Bird’s home (4)
10. Number of seats on a tandem (3)
12. Butter commonly used in cosmetics (4)
16. Up to this moment (3)
20. Creator of Tom Sawyer (5)
22. Pair (3)
26. Crème-filled biscuit brand (4)
28. Noise of disgust? (3)
32. Veracious (4)
35. Bovine utterance (3)
37. Beer barrel (3)
42. Historical age (3)
45. Lair (3)
47. Baby's dinnertime protection? (3)
49. Vegetable, pak ____ (4)
52. Precedes 'drome', 'plane' and 'dynamic' (4)
55. South American capital (4)
MYSTERY SONG:
BLANK [30DR] [15DL] [33DL] BLANK [34DL] BLANK [8DL] [53DR] BLANK [21A] BLANK [61DL] [6DR] [62DR] BLANK [61DL] BLANK [7A] [58DR] BLANK [56A] [48DL] BLANK [30DR] [14A] BLANK [40A] BLANK [38DR] [21A] BLANK [34A] [51A] BLANK [3DL] [2DL] BLANK BLANK BLANK BLANK [18DR] BLANK [56DL] BLANK [41A] BLANK BLANK [36DL] [17A] [46DL] BLANK [58DR] BLANK [57DL] [31A] BLANK BLANK BLANK [25DL] [61DL] BLANK BLANK BLANK BLANK BLANK [50A] [30DR] BLANK BLANK [34A] BLANK BLANK BLANK [29A] [57DL] [5A] BLANK [30DR] [15DL] [33DL] BLANK [24DL] BLANK BLANK BLANK BLANK