Add water and sugar to a pot and bring to a boil for 3 minutes.

In a separate container, beat the yolks until light and fluffy. While beating, gradually add the sugar water and continue to whip for 1 minute.

Add the white chocolate and butter to the yolk mixture.

Pour in the Limoncello and stir until well mixed.

Fold in the mascarpone cheese to the white chocolate mixture.

In another bowl, whip the cream to stiff peaks and fold it into the chocolate mixture.

Add lemon zest and gently mix. Pour the mousse into ramekins or glasses of your choice.

Refrigerate for 6 hours, or preferably overnight. Garnish with candied lemon and white chocolate before serving.