Chocolate Pudding

1 ¼ cups sugar
½ cup cocoa
¼ cup cornstarch
½ tsp salt
2 ½ cups milk
1/3 cup unsalted butter, cut up
2 tsp vanilla
Unsweetened whipped cream

Whisk together first 4 ingredients in a medium saucepan.  Gradually whisk in milk.  Cook over medium heat, stirring constantly, until pudding boils and is thickened (about 8 to 10 minutes.)  Reduce heat to medium low, and cook 2 more minutes.  Remove from heat; add butter and vanilla, stirring gently until butter melts.  Place heavy-duty plastic wrap directly on warm pudding (to keep a film from forming); cool 10 minutes.

Serve warm or chill until ready to serve.  Top with whipped cream.