Place egg yolks and water in a small saucepan over low heat
Stir constantly until thick, coats the back of spoon and reaches 160 F on a thermometer. Place over ice to cool.
In another bowl combine brown sugar, vanilla extract, and egg yolks.
Beat in mascarpone and set aside.
In a double boiler place egg whites, white sugar, and cream of tartar.
Whisk constantly until thermometer reaches 160 F.
Pour into a bowl. With an electric mixer, whip to soft peaks.
Fold gently into mascarpone.
Fill the crepes with filling