1. For almond crust, in a small bowl combine almonds and brown sugar. Place a portion at a time in a food processor bowl or blender container; cover and process or blend until nuts are finely ground. Transfer to a medium bowl. Stir in flour. Add butter, stirring until well combined. Press mixture onto bottom and 1 inch up side of a 9-inch tart pan with a removable bottom or a 9-inch springform pan. Bake in a 325 degree F oven about 20 minutes or until golden and firm to the touch. Cool crust in pan on a wire rack.
2. In a small saucepan beat whipping cream over medium heat just until simmering. Remove from heat; whisk in semisweet chocolate until smooth. If desired, whisk in Grand Marnier. Cool about 30 minutes or until filling begins to thicken but is still pourable. Spread marmalade over bottom of crust. Pour chocolate filling over marmalade. Cover and chill in refrigerator about 2 hours or until set.
3. To serve, remove side of pan. Use a sharp knife to cut tart into wedges. If desired, garnish each wedge with a kumquat half and a sprig of fresh herb. Makes 10 to 12 servings.