In a sauce pan, add the condensmilk, butter, milk, sugar and vanilla. Stir for 50 minutes over medium heat until the color changes. The fudge will form a ball.
Remove from the heat. add the white chocolate, lemon zest and juice. Mix quickly before it solidifies.
Pour the fudge into a greased baking tray.
For the Topping
In a double boiler, melt the dark chocolate and cream.
Pour over the fudge. Garnish with white chocolate shavings.