Preheat oven to 350º. Grease & lightly flour a 9” springform pan.
In a large bowl, combine flour, sugar, cocoa, baking soda, and salt. Set aside.
In a medium bowl, whisk eggs, milk, liqueur, oil, vinegar, and vanilla. Add egg mixture to dry ingredients, stir until well blended.
In a medium bowl. Combine cream cheese and melted chocolate until well blended. Beat Cream cheese mixture into batter. Pour batter into prepared pan. Bake 45-50 min or until pick inserted in center comes out clean. Cool in pan 10 min, remove sides of pan and cool completely. Invert onto a serving plate.
Frosting: Melt Chocolate and butter over low heat in a medium saucepan, stirring constantly. Remove from heat; add sugar and vanilla. Stir until crumbly. Add water and stir until smooth. Adding a teaspoon more of Hot water if needed.
Spread frosting over cake. Garnish with chopped walnuts if desired or sprinkle with Confectioners sugar.