Whisk together sugar, cornstarch, and 1/8 tsp salt in a heavy medium saucepan, then whisk in milk and cream. Bring to a boil over medium heat, whisking frequently, then boil, whisking, 1 minute. Remove from heat and whisk in butter and vanilla.
Divide among 4 (6- to 8-oz) glasses and chill, uncovered, until cold, at least 1 1/2 hours.
Stir together preserves, brandy, and lemon juice, then spoon on top of puddings.
