Scald half-and-half in top of a double boiler over boiling water.
Beat eggs in a medium mixing bowl until light and fluffy. Combine sugar and cornstarch; add to eggs, beating well. Gradually stir one-third of warm half-and-half into egg mixture; add to remaining half-and-half in top of double boiler, stirring well.
Cook over boiling water, stirring until mixture thickens and coats a spoon. Remove from heat; stir in vanilla. Cool completely; chill thoroughly. Spoon over strawberries and raspberries in individual serving dishes.