Rinse a heavy medium saucepan with cold water and shake out the excess (this helps prevent the milk from sticking). Add 2 cups of the milk and bring to nearly a boil over moderate heat.

In a medium bowl, whisk together the eggs yolks, brown sugar, cornstarch and remaining 1/2 cup milk until well blended.

Gradually pour 3/4 cup of the hot milk into the egg yolk mixture, 1/4 cup at a time, whisking vigorously after each addition. Return this mixture to the remaining hot milk in the pan and cook over moderate heat, whisking constantly, until the custard begins to simmer and thicken slightly, about 2 minutes. Remove from the heat and whisk in the butter and vanilla.

Strain the pudding into a bowl, scraping it from the bottom of the sieve. Spoon the pudding into individual serving bowls or glass sundae dishes. To avoid pudding "skin, " lay a piece of waxed paper or plastic wrap directly on the surface. Let cool on a wire rack for 10 minutes, then refrigerate for at least 50 minutes. Serve with a dollop of whipped cream.