Step 1
In a large mixing bowl cream together 1/2 cup softened butter and 1/4 cup sugar until pale about 3 minutes; beat in egg.
Step 2
In a separate bowl mix flour and cocoa powder. Using a wooden spoon stir the dry ingredients into the creamed mixture and gather the dough into a ball. Flatten the dough into a disk and wrap in waxed paper; refrigerate for at least 2 hours.
Step 3
Preheat oven to 325 degrees F (165 degrees C).
Step 4
On a lightly floured surface roll out chilled dough into a 10 inch round and about 1/4 inch thickness. Transfer dough to an 8 inch tart pan pressing dough evenly into pan; prick all over with a fork and freeze for 10 minutes.
Step 5
Bake tart shell in preheated oven for 12 minutes; transfer to a rack to cool.
Step 6
To make caramel: In a small saucepan over low heat bring 1/2 cup heavy cream to a simmer. In a heavy medium saucepan over high heat gradually add 1/2 cup sugar in small amounts stirring constantly until it melts and turns golden brown. Remove saucepan from heat and slowly stir in hot cream; stir in 2 tablespoons butter and allow mixture to cool.
Step 7
To make chocolate cream: In a medium bowl combine semisweet chocolate and liqueur. In a small saucepan over high heat bring remaining 1/2 cup heavy cream to a boil and pour it over chocolate; stir mixture with a wooden spoon until chocolate is melted and very smooth.
Step 8
Reserve 13 whole macadamia nuts and chop the rest. Pour cooled caramel into the cooled tart shell and spread evenly with a metal spatula; sprinkle chopped nuts over caramel. Pour chocolate cream on top and spread evenly.
Step 9
Arrange 10 whole nuts around the edge of the tart to mark 10 slices; place remaining 3 nuts in the center. Refrigerate the tart for 1 hour or until firm; serve.