- With the rack in the middle position, preheat the oven to 350°F (180°C). Butter an 8-inch (20 cm) square baking dish and line the bottom with a sheet of parchment paper, letting the paper hang over two sides.
- In a bowl, combine all the ingredients until the mixture sticks together. Press onto the bottom of the prepared dish.
- Bake for 10 minutes or until the crust begins to firm up.
- Meanwhile, in a saucepan off the heat, combine the sugar and cornstarch. Whisk in the pineapple and lemon juice. Bring to a boil over medium heat, whisking constantly and scraping the bottom and sides of the pan until the mixture thickens, about 7 minutes.
- Spread the mixture over the crust, then sprinkle with the coconut. Bake for 20 minutes. Let cool completely.
- Cut into bars. The pineapple and coconut bars will keep for 1 week in an airtight container in the refrigerator.