Butterscotch Pudding

* 1/2 cup packed dark brown sugar
* 2 tablespoons plus 2 tsp cornstarch
* 1 1/2 cups whole milk
* 1/2 cup heavy cream
* 2 tablespoons unsalted butter, cut into bits
* 1 teaspoon pure vanilla extract

*Accompaniment:
lightly sweetened whipped cream

Whisk together brown sugar, cornstarch, and 1/4 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. Pour into a bowl, then cover surface with buttered wax paper and chill until cold, at least 1 1/2 hours.