• In a saucepan, whisk together cream, coffee (or water), vanilla, and egg yolks until smooth.
• Stir mixture continuously over low heat until it just reaches 165°. Remove from heat immediately. Add chocolate and stir until smooth. Set aside in the refrigerator.
• In a double boiler, whisk together egg whites and sugar. *Use a very clean whisk as any trace of grease will impede development of meringue.* Continue to whisk while heating very slowly to a temperature of 165°. Remove from heat immediately.
• Add cream of tartar to egg white mixture and beat with an electric hand mixer until stiff peaks form.
• Remove chocolate mixture from the refrigerator and whip with an electric hand mixer until the mixture lightens in color and thickens.
• Gently fold half of meringue into the chocolate mixture until almost completely incorporated. Add other half of meringue and fold gently until incorporated fully.
• Immediately pour mousse into 8 dessert cups and refrigerate for at least 2 hours. Top each serving with a dollop of sweetened whipped cream immediately before serving.

Sweetened Whipped Cream

• Pour all ingredients into a bowl and beat with an electric hand mixer until soft peaks form.