This pretty cake is decorated with glazed apricot slices and toasted almonds.
Heat oven to 325 degrees. Place sliced almonds on a baking sheet, and toast until golden brown, 5 to 10 minutes. Set aside.
Coat an 8-inch-round pan (2 inches high) with butter. Line with parchment paper, butter, and flour; set aside.
Combine flour and baking powder in a small bowl; set aside. Place almond paste, sugar, and 5 tablespoons butter in the bowl of an electric mixer fitted with the paddle attachment; beat on medium speed until well combined, about 2 minutes. Add eggs and Grand Marnier, if using; process until smooth. Transfer to a large bowl; fold in flour and baking powder.
Pour batter into prepared pan; bake 40 minutes, until golden brown and a cake tester comes out clean. Place on a rack to cool in pan for 10 minutes. Turn cake out of pan onto rack; cool completely.
Heat marmalade with 1 tablespoon water in a small saucepan. Arrange apricot slices on top of cake; brush with apricot marmalade. Garnish with toasted almonds.