For custard, in a small saucepan thoroughly combine the first 2 tablespoons sugar and the cornstarch. Add the milk and beaten egg. Cook over medium heat stirring the mixture with a wooden spoon just until mixture begins to bubble. (Do not overcook.) Immediately pour the custard out of the saucepan and into a small bowl; let mixture cool about 5 minutes.
Whisk the light sour cream into the custard; add the vanilla. Cover and thoroughly chill the custard for up to 24 hours.
At serving time, rinse the berries; drain well. Divide berries evenly among four dessert dishes, custard cups, or goblets. Spoon chilled custard over berries in dishes. (If necessary, thin custard with a little milk before spooning over berries.) Set desserts aside.
For topping, in a small skillet or saucepan heat the remaining 2 tablespoons sugar over medium-high heat until sugar just begins to melt, shaking skillet occasionally to heat evenly (but do not stir). Reduce heat to low and cook until sugar is melted and golden, stirring as necessary with a wooden spoon after sugar begins to melt. Quickly drizzle the caramelized sugar over each dessert serving. Serve immediately. Makes 4 servings.