How do I solve 5 down in Times Cryptic 29540?

Question

Accepted Answer

5 down reads "Sponge cakes go flat in the end" (3 letters); the answer is SOT. It's a letter-selection clue: take specific letters from a longer source. 'First of' means the opening letter, 'extremely' means first + last, 'regularly' means every other letter, 'oddly' / 'evenly' means odd or even positions. The full step-by-step breakdown is on this page.

Sponge cakes go flat in the end (3)

5D — Sponge cakes go flat in the end (3) — SOT