Place finely chopped chocolate in a large, heat resistant mixing bowl. (Note: Chocolate must be very finely chopped so it melts quickly)
In a heavy 1½ to 2 quart saucepan, whisk the egg yolks. Whisk in the granulated sweetener.
Gradually, a tablespoon at a time, whisk in one cup of the heavy whipping cream (keeping 1 cup for later). Place the saucepan over low heat and monitor the temperature using a candy thermometer. Whisk constantly while the mixture heats.
When the egg yolk and cream mixture reaches 160º Fahrenheit, remove from heat immediately and pour, all at once over the chopped chocolate. Allow to sit for a minute, then stir until mixture is glossy and smooth. Refrigerate until room temperature, stirring frequently. This doesn't take very long--only about the amount of time it takes to clean up the kitchen and whip the cream for the next step. Mixture does not need to be cold, but it shouldn't be warmer than room temperature. Do not over-chill it or it will get too hard to make the mousse.
While mixture is cooling, pour the remaining one cup of heavy whipping cream into a medium mixing bowl. Beat, using a hand mixer, until soft peaks form. Add the vanilla extract and beat until firm, (but not stiff) peaks form.
Remove the chocolate mixture from the refrigerator and gently stir ⅓rd of the whipped cream into the chocolate mixture. Fold in the remaining ⅔rds.
Spoon the mousse into 8 dessert dishes, dividing it equally among the dishes. I used dessert dishes that hold ½ cup. Chill for 2-3 hours before serving.
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