1. Pre heat oven to 180°C/350°F/ Gas 4. Lightly grease a large 6 cup muffin tray.
2. Drain pineapples: reserve juice and make up the 200ml (for cake mix) with water if necessary.
3. Divide the sugar evenly between the muffin cups, then pour into each the melted margarine, again having it evenly divided.
4. Arrange a pineapple ring over the sugar mixture in each cup.
5. Prepare the cake mix according to package directions, replacing water with reserved juice. Evenly pour batter into muffin cups.
6. Bake for 20 to 25 minutes, until well risen and springy to the touch.
7. Cool for 5 minutes. Cut top off each bun. Loosen edges with a knife and turn onto serving plate.
8. Serve each cake with a dollop of cr̬me fraiche with the top of the bun and a sprig of mint sitting on it.

Notes:

If muffin tin is not available, use ordinary bun tin and just half a pineapple ring in each cup.