One 14-ounce can unsweetened coconut milk, stirred
1/2 cup sugar
2 tablespoons light corn syrup
6 tablespoons unsalted butter
11 ounces bittersweet chocolate, chopped and melted
Preheat the oven to 350°. Spread the shredded coconut on a baking sheet and toast until lightly golden, about 4 minutes. Let cool completely.
In a medium saucepan, combine the coconut milk with the sugar, corn syrup and 4 tablespoons of the butter. Cook over moderately low heat, stirring frequently, until thick as jam, about 40 minutes. Remove from the heat and whisk in the remaining 2 tablespoons of butter and the toasted coconut. Transfer to a bowl and let cool.
Cover a baking sheet with wax paper. Using an offset spatula, spread half of the melted chocolate on the wax paper in a 10-by-7-inch rectangle. Refrigerate until firm, about 10 minutes. Spread the coconut mixture over the chocolate and refrigerate until set, about 10 minutes. Spread the remaining melted chocolate over the coconut and refrigerate until firm, about 20 minutes. Trim the edges of the rectangle, then cut into 40 squares. Cover and refrigerate until serving.
The candy bars can be refrigerated for up to 1 week.