In a small bowl, beat the egg yolks until they are a pale yellow.
Melt the chocolate with the coffee using a double boiler or a metal boil over boiling water.
Remove from heat, and mix with a beater or wire whisk, adding the egg yolks a little at a time.
Add the brandy.
In a separate bowl, whip the egg whites until they are foamy and hold soft peaks.
Mix two tablespoons of the whipped egg whites into the chocolate mixture.
Gently fold in the rest of the egg whites.
Pour the mixture into a glass bowl or individual serving dishes and chill in the refrigerator for a few hours. The mousse will thicken up as it chills.
Notes
If you are using this a filling for cupcakes, it will fill all 16 with some leftover for snacking.