Step 1Heat the oven to 350 degrees. Butter and flour a 9-inch round cake pan.
Step 2Beat together the butter and sugar until light and creamy, about 4 minutes. Stir the cocoa and water together in a bowl and add to the butter mixture. Beat 7 minutes, scraping down the sides of the bowl often. Add the flour, salt, baking powder and baking soda. Beat 2 minutes longer. Add the eggs. Mix until the batter is shiny and smooth, 5 minutes, scraping down the sides of the bowl.
Step 3Pour the batter into the pan. Bake the cake until the center springs back when lightly touched, about 40 minutes. Invert the cake onto a wire rack to cool completely.
Step 1Bring the whipping cream to a simmer. Remove from the heat. Stir in the chocolate pieces until smooth.
Step 2Remove 1 1/2 cups of the ganache and set aside at room temperature. Refrigerate the remaining 1 cup until thick and creamy, 1 hour.
Step 1Split the cake into 3 horizontal layers. Drizzle the orange-flavored liqueur over each layer. Frost the layers with the chilled Ganache. Pour the remaining Ganache over the top. Garnish with the oranges.