In a double boiler over medium-high heat, melt chocolate and butter.
You can also melt in the microwave on medium setting but monitor every few seconds so the chocolate does not burn.
Dissolve instant coffee in the 1/4 c water.
In a large bowl, combine powdered sugar, egg yolks, kahlua and coffee.
Gently fold in the chocolate mixture.
In another bowl, whip cream until stiff peaks form.
Again gently fold the whipped cream into chocolate mixture.
In a small bowl, beat egg whites until stiff, then fold into the chocolate mixture.
Pour into 4 serving glasses or cups.
Cover with plastic and refrigerate for about 4 hours.