How to Make It
In a heavy, medium saucepan, combine the sugar, water, corn syrup and lemon juice and bring to a boil. Stir the mixture once and simmer over moderate heat until a light amber caramel forms, about 8 minutes. Remove from the heat and carefully stir in the cream and butter. Return the sauce to high heat and stir constantly until smooth and glossy, about 1 minute. Remove from the heat. Rewarm before serving.
Preheat the oven to 400°. Arrange the pineapple rings on 2 large rimmed baking sheets. Pour the pineapple juice over them and sprinkle with the sugar. Bake the pineapple rings for 1 hour, or until dark brown on both sides; turn the rings and rotate the baking sheets every 20 minutes for even browning. Let the rings cool on the baking sheets.
To serve, arrange 2 halved pineapple rings in each of 8 tall glasses or serving bowls and top with scoops of vanilla ice cream. Drizzle with the caramel sauce and garnish with the Macadamia Brittle.