1Grease 9-inch square pan with shortening or cooking spray. In large microwavable bowl, microwave 3 tablespoons butter uncovered on High until melted. Stir in espresso powder and coffee liqueur until well combined.
2Add marshmallows to butter mixture. Microwave uncovered on High 45 to 60 seconds or until marshmallows are melted. Stir in chocolate chips until chocolate is melted and marshmallows are smooth. Stir in cereal until well combined. Press mixture in pan. Refrigerate about 1 hour or until set.
3In 2-quart microwavable bowl, microwave vanilla baking chips uncovered on High about 60 seconds or until chips can be stirred melted and smooth. Add powdered sugar, 1/3 cup softened butter, the vodka and salt; beat with electric mixer on medium speed until smooth.
4Spread frosting over cereal bar base. Sprinkle with chocolate shavings. Store covered in refrigerator. For bars, cut into 4 rows by 4 rows.