In a medium pan over high heat, bring to boil milk and water. Reduce heat to simmer liquid. Stirring constantly, pour in polenta in a thin, steady stream, breaking up any lumps that form. Stir in 2 tablespoons sugar and salt. Simmer, stirring often, until polenta is soft and creamy, about 30 minutes.
In a small bowl, mix sour cream and 1 tablespoon sugar.
Ladle polenta into bowls, and top with about 1 tablespoon of jam and a dollop of sweetened sour cream.