In a large bowl, using an electric mixer, cream the butter and sugar until pale, about 3 minutes. Beat in the egg. In a separate bowl, stir the flour and cocoa. Using a wooden spoon, stir the dry ingredients into the butter-sugar mixture and gather the dough into a ball. Flatten the dough into a disk, wrap in wax paper and refrigerate for at least 2 hours.
Preheat the oven to 325°. On a lightly floured surface, roll out the chilled dough into a 10-inch round, slightly less than 1/4 inch thick. Transfer the dough to an 8-inch tart pan, pressing the dough evenly into the pan. Prick all over with a fork and freeze for 10 minutes.
Bake the tart shell for 12 minutes. Transfer to a rack to cool.
In a small saucepan, bring the heavy cream to a simmer over low heat. Set a heavy medium saucepan over high heat and gradually add the sugar in small amounts, stirring constantly, until it melts and turns golden brown. Remove the saucepan from the heat and slowly stir in the hot cream. Stir in the butter and let cool.
In a medium bowl, combine the chocolate and coffee liqueur. In a small saucepan, bring the heavy cream to a boil and pour it over the chocolate. Using a wooden spoon, stir the mixture until the chocolate is melted and very smooth.
Reserve 13 whole macadamia nuts; crush the rest. Pour the cooled caramel into the cooled tart shell and spread evenly with a metal spatula. Sprinkle the crushed macadamia nuts over the caramel. Pour the chocolate cream on top and spread evenly. Arrange 10 whole macadamia nuts around the edge of the tart to mark 10 slices; place the remaining 3 nuts in the center. Refrigerate the tart for 1 hour, or until firm.