Line a 9 inch pie pan with the pastry, forming a high edge. Crimp edges attractively. Refrigerate pastry shell while making the filling.
Preheat oven to 350. In small pan, over medium low heat, melt butter and chocolate. Let cool slightly.
In small bowl with mixer on high, beat eggs til foamy. Gradually beat in sugar in a thin stream til eggs are thick and lemon colored. Reduce mixer speed to slow
Beat in melted chocolate, then the liqueur and the vanilla. Fold in the flour, blended with the salt
Scatter chopped nuts in bottom of the pie crust. Pour the filling over the nuts.
Bake pie til crust is golden and filling is no longer jiggly, about 35 minutes. Cool completely on wire rack. Serve with small scoops of ice cream or with whipped cream flavored with additional Irish cream liqueur.