Place the cream and half of the sugar into a small saucepan and heat over low heat. Stir occasionally. Meanwhile, in a medium bowl, place the egg yolks, lemon zest, lemon juice, cornstarch, and remaining sugar and whisk well. When you see small bubbles in the cream mixture, after about 4 to 5 minutes, remove from the heat and pour a little into the bowl with the egg yolk mixture. Whisk well. Add half of the remaining cream mixture and whisk. Add the remaining cream mixture and whisk in. Add the yogurt or labne and whisk well. Strain into another bowl and press as much liquid as possible through the sieve.