Preheat the oven to 180°C.
Scatter the rhubarb over a baking sheet, coat with the sweetener and cover with tin foil.
Place in the oven and cook for about 20 minutes. The aim is to have soft rhubarb that holds its shape and has released its juices, but it can fall suddenly. Don't worry if this happens. It will still taste fab.
Drain the juice into a small bowl and stir in the gin (or apple juice).
Break up one sponge finger into the bottom of each trifle dish, add a spoonful of juice and then a layer of rhubarb.
Repeat with another layer of sponge, juice and rhubarb. Spoon over a little more juice if the sponge looks too dry. Cover and refrigerate while you make the custard.
Pour the milk into a small saucepan and place over a medium to high heat, until it just starts to boil. Keep an eye on it as it can boil over very quickly!
Whisk together the egg yolks, sweetener, vanilla and cornflour until smooth.
When the milk has come to the boil, remove from the heat.
Whisk the milk into the egg mixture. Do this a little at a time to begin with to temper the eggs. If you pour it in too fast, the eggs may scramble. As the heat from the milk warms the eggs, you can pour the milk in faster, whisking all the time.
Pour the custard back into the saucepan and return to a low heat, stirring all the time, until it thickens and bubbles break the surface. Cook for around 2 minutes, and taste to ensure the cornflour has cooked out and the mix doesn't taste powdery.
Remove the trifles from the fridge and pour the custard evenly over. Cover and chill for at least 2 hours until set.
When you are ready to serve, spray 25g of light aerosol cream on top and sprinkle over the crushed biscuit for decoration. Enjoy!