While by no means "light", this decadent mousse uses yogurt to help reduce some of the cream in this classic French recipe.
Heat 1 cup of cream in a 1-quart heavy saucepan until hot.
Whisk together yolks, sugar and a pinch of salt in a metal bowl until combined well.
Add in hot cream in a slow stream, whisking until combined.
Transfer mixture to saucepan and cook over moderately low heat, stirring constantly, until it registers 160Â°on thermometer.
Pour custard through a fine-mesh sieve into a bowl and stir in vanilla.
Melt chocolate in a double boiler or a metal bowl set over a pan of simmering water, or in a glass bowl in a microwave at 50 percent power 3 to 5 minutes, stirring frequently.
Whisk custard into melted chocolate until smooth, then cool.
Beat remaining 1/2 cup of cream in a bowl with an electric mixer until it just holds stiff peaks.
Fold vanilla yogurt into the whipped cream.
Whisk one fourth of this mixture into chocolate custard to lighten, then fold in remaining yogurt and cream mixture gently but thoroughly.
Pour into bowls or glasses and chill at least 6 hours.
Let stand at room temperature about 20 minutes before serving.