1. Bring 2 cups water to a boil in a medium saucepan. Meanwhile, cut the peel off grapefruit, removing pith. Slice peel into thin pieces and boil about 2 minutes. Drain and return to saucepan with 1/2 cup water and 1/2 cup sugar. Bring to a boil, reduce heat and simmer until tender, about 6 minutes. Drain and sprinkle with 1 tablespoon sugar. Melt chocolate in a heat-proof bowl set over a pan of simmering water, stirring occasionally, until smooth. Line a baking sheet with wax paper. Pour chocolate over paper and spread with a spatula to form a 1/4-inch-thick rectangle. Sprinkle with peel, roasted cashews and a pinch coarse sea salt; refrigerate 30 minutes or until firm. Break into pieces and serve at room temperature.