Prepare an 8-inch square baking pan by greasing it.
Melt chocolate and butter in medium, heavy saucepan over low heat (I use a double boiler). Remove from heat. Stir in sugar. Whisk in eggs, one at a time, mixing well after each addition. Whisk in liqueur.
Combine flour, baking powder and salt in small bowl; stir into chocolate mixture until just blended.
Spread batter evenly in prepared pan.
Bake 22 to 25 minutes or until toothpick inserted in center comes out clean. Remove pan to wire rack; cool completely.
Add cream cheese and butter to small bowl and beat with electric mixer at medium speed until smooth. Beat in liqueur. Gradually beat in powdered sugar until smooth.
Spread over cooled brownies.
Chill at least 1 hour or until frosting is set. Cut into 2-inch squares.