Preheat oven to 350°.
Spray 9-inch springform pan.
Chop chocolate into small pieces.
Put 1/2 pound chocolate into the top of a double boiler with the butter.
Stir over medium heat until chocolate melts.
Set aside to cool.
Bowl should be warm and not hot to touch.
In large bowl with electric mixer, start mixing egg yolks.
Add sugar and mix until liquid is thick - about 3 minutes.
Slowly mix in melted chocolate and 3 Tbsp of creme de menthe.
In another bowl, whip the egg whites with a pinch of salt until they form soft peaks.
Fold in chocolate mixture.
Transfer ingredients into pan and bake for 40 minutes.
Remove outer ring of pan and cool on rack (cake may have cracks on top and will settle).
In a heavy pan over low heat, melt remaining chocolate with 1/2 cup cream to make icing.
Use while warm to ice cake.
Refrigerate for 30 minutes before serving.
Whip 1 cup cream with 1 Tbsp creme de menthe as optional topping or serve with fresh raspberries.