Grease and line a large oven tray.
2 Peel and trim pineapples; reserve half the trimmings. Halve pineapples lengthways; cut each half into four wedges. Cut out the core from each piece; reserve core pieces. Thread pineapple pieces onto metal skewers. Pat pineapple dry with paper towel.
3 Preheat a chargrill plate or barbecue on high; cook pineapple skewers for 1 minute each side or until grill marks appear. Transfer pineapple to lined tray.
4 Crush star anise using a mortar and pestle (or use the base of a clean saucepan). Place in a medium heavy-based saucepan with sugar, reserved pineapple cores and trimmings, and ¼ cup (60ml) water; cook over low heat, stirring, until sugar dissolves. Increase heat to medium; cook, without stirring, for 15 minutes or until a golden brown caramel forms, swirling the pan to colour evenly.
5 Preheat oven to 200°C/400°F.
6 Taking care, as the mixture will splutter, add ¾ cup of the rum to the caramel. Increase heat to high; boil for 2 minutes or until syrupy. Add butter and 1 cup (250ml) water; boil for 10 minutes until thick. Add remaining rum; cook for a further 2 minutes. Strain into
a heatproof jug; discard solids.
7 Brush pineapple with rum syrup. Roast pineapple in oven, basting every 10 minutes with the syrup, for 45 minutes or until tender and caramelised. Cool slightly. Cut limes into cheeks or wedges.
8 Serve pineapple skewers drizzled with roasting juices and any remaining syrup; top with mint leaves and lime cheeks.