Mix the orange juice with the liqueur and the icing sugar.
Thoroughly combine the Mascarpone, quark, milk and icing sugar.
Arrange half the Panettone slices in the tin. Drizzle over half the liquid. Top with the oranges. Distribute half the Mascarpone mixture over the oranges. Top with the remaining slices of Panettone and drizzle over the remaining liquid. Top with the remaining Mascarpone mixture. Cover and refrigerate for approx. 4 hrs. Dust the tiramisù with cocoa shortly before serving.