Put the lemon zest, lemon juice, and sugar into a medium saucepan.
Heat the mixture over medium heat, stirring constantly, until the sugar has dissolved. You should not feel any remaining grittiness. Set the pan aside.
In a new saucepan heat the cream and mascarpone over medium heat, stirring to melt the mascarpone. Bring it just barely to a simmer, do not boil!
Remove the pan from the heat, and whisk in the lemon mixture. Strain through a fine mesh sieve and the pour into 4-6 small bowls or glasses.
Chill the lemon cream until firm. This will take about 8 hours, and you can make them the day ahead and chill them overnight. The lemon cream will last 3 days, refrigerated.
