Soften the gelatine leaves in cold water.
In a heavy-based saucepan, mix the milk, cream, sugar and limoncello liqueur. Gently simmer, remove from the heat and add the gelatine leaves.
Stir until the gelatine has dissolved and pour into dariole moulds. Leave to cool, then place in the fridge to set.
To make the sauce, place the butter and sugar in a saucepan over a gentle heat and allow the butter to melt and sugar dissolve.
Add the chopped strawberries and lemon juice. Remove from the heat and pass through a sieve. Allow to cool.
Turn the panna cotta out onto individual serving plates and spoon the strawberry sauce all around. Decorate with a slice of lemon dipped in icing sugar.
