To make the tiramisu:

Bring the water to a boil and add the sugar and lemon balm. Boil for 2 minutes, allow to cool and strain the syrup through a conical sieve.

Place half of the sponge finger biscuits into the base of the roaster and pour over half of the syrup. Set aside to allow the syrup to be absorbed.

Mix the mascarpone with the Limoncello.

Beat the egg yolks and the sugar with a hand whisk or in a food processor until light and airy. Combine this with the mascarpone mixture.

Beat the egg whites until stiff and fold them into the mixture.

Pour half the mascarpone mixture over the biscuits.

Add a second layer of biscuits, pour over the remaining syrup and cover with the remaining mascarpone mixture.

Place in the refrigerator to set for about 4 hours.

To make the topping: If using, coarsely crush the boiled sweets in a pestle and mortar.

Decorate the tiramisu with the strawberries, lemon balm leaves and the (optional) crushed sweets just before serving.