You can either top this with the top half of the biscuit or cut the top half in 6 and use to top each plated serving with a rectangle of shortcake. Serve immediately.
Fold half into the custard. Coarsely break 6 of the biscuit and place in a trifle bowl. Add half the rhubarb. Spread over half the custard cream and then slice up half the jelly. Repeat and then ...