Wash the limes with hot water and rub the peel off. Squeeze the limes and lemons. Mix the juice and half of the zest with the mascarpone, yogurt and sugar. If you like, add some sugar.
Place half of the ladyfingers in a baking dish (approx. 15 cm) and drizzle with liqueur as desired. Spread half of the cream on top. Cover with the remaining ladyfingers and top with the remaining cream.
Sprinkle the tiramisu with the rest of the lime zest and refrigerate overnight.