In a medium bowl, beat the milk, eggs and sugar with an electric mixer on low speed or by hand with a wire whisk.
Pour in a 1 1/2-quart heavy bottom saucepan. Cook over low heat until the mixture thickens (do not boil) and a thermometer reads 160 degrees, stirring constantly with a heat-proof rubber scraper or wire whisk. Remove from the heat.
Stir in the semisweet and bittersweet chocolate until melted and smooth. Fold in the sour cream. Pour into 8 (1/4-cup) dessert bowls or glasses.
Refrigerate for 1 hour or until completely chilled. Garnish each serving with a strawberry half and a light sprinkle of powdered sugar.