Bake a 9" pie crust and cool. Cream butter and sugar until light and fluffy. Beat in the chocolate, and vanilla. Add 1 egg and beat at medium speed for 5 minutes, using the paddle attatchment. Scrape the bowl. Add the 2nd egg and beat for an additional 5 minutes. Mixture should be light and fluffy and smooth. Pour into the crust and smooth with a spatula. Refrigerate at least 2 hours, until firm. Serve cold, with whipped cream. May garnish with chcolate shavings if you want.