Add milk to egg yolks and beat with rotary beater.
Mix ½ c. sugar and cornstarch; add to milk and eggs. Cook in top of double boiler or over low heat until thickened, stirring constantly. Remove from heat. Reserve 1 c. of mixture.
Add gelatin to remaining mixture and stir until gelatin is dissolved.
Melt 1½ squares chocolate and add to reserved cup of cream filling. Add 1 tsp. vanilla and beat with rotary beater. Cool. Pour chocolate filling into pie shell and chill.
Beat egg whites until frothy; add cream of tartar and beat until stiff; add remaining sugar gradually, beating until stiff. When gelatin mixture is slightly thickened, fold in egg whites and remaining vanilla.
Pour into pie shell, covering the chocolate layer. Chill thoroughly. Grate remaining ½ square chocolate. Sprinkle over top.