1. In a large mixing bowl, beat mascarpone, coconut milk, powdered sugar, and vanilla until smooth and creamy. 2. In another bowl, whip heavy cream to soft peaks, then fold into mascarpone mixture until fluffy. 3. In a shallow dish, combine cooled coffee and coconut rum. Quickly dip each ladyfinger in the mixture and arrange a layer in the bottom of a 9×13 inch dish. 4. Spread half of the coconut mascarpone cream over the ladyfingers. Repeat with another layer of dipped ladyfingers and the remaining cream. 5. Cover and refrigerate at least 4 hours or overnight. 6. Before serving, dust with cocoa powder and sprinkle toasted coconut on top. Garnish with mint or tropical fruit if desired.