Prepare Hazelnut Crust; set aside.
Combine butter and semisweet chocolate in a small saucepan; place over medium-low heat. Cook until chocolate and butter melt, stirring until smooth. Cool 10 minutes.
Combine flour and salt; stir well, and set aside.
Combine eggs and sugar in a mixing bowl, and beat at medium-high speed with an electric mixer 3 minutes or until thick and pale. Add cooled chocolate mixture and vanilla; beat well. Add flour mixture, stirring well. Stir in Frangelico.
Pour chocolate batter over crust. Bake at 350° for 32 minutes. (Top will appear cracked.) Place pan on a wire rack. Immediately arrange milk chocolate squares in rows over uncut brownies. Sprinkle with hazelnuts. The heat of the brownies will partially melt the chocolate squares, helping them to "frost" the brownies and hold the nuts on top. Cool and cut into 16 squares.