Identify the dish: quick-soak desserts (tiramisu-style) need high-absorbency; layered trifles need structural crumbs.
Pick the substitute in the table that matches your target texture (soft soak vs firm layer).
Use the stated ratio; for cake swaps, start at the lower end (¾) because cake absorbs faster than cookies.
Moisten in the filling just long enough to soften the outside: assemble and chill immediately so layers set without turning to paste.
Taste after a 5–10 minute soak window: add a quick pinch of cocoa/sugar to balance if the substitute reads bland.