1/2 cup crunchy toffee pieces, such as broken Heath or Skor bars
In a large, heavy saucepan, melt the butter. Add the brown sugar and cook over low heat, stirring, until the sugar is dissolved and bubbling, about 3 minutes. Stir in the warmed cream.
In a small bowl, combine the cornstarch with the salt. Add 1/2 cup of the milk and whisk until smooth. Add the cornstarch mixture to the saucepan along with the remaining 1 1/2 cups of milk and cook over moderate heat, stirring constantly, until thickened, about 4 minutes. Off the heat, whisk in the egg yolks, 1 1/2 teaspoons of the vanilla and the bourbon. Return the pudding to the heat and bring to a boil, stirring constantly. Off the heat, whisk in the vinegar. Strain the pudding through a fine sieve set over a bowl. Pour the pudding into six 6- to 8-ounce parfait glasses or dessert bowls. Press a piece of plastic wrap directly on the surface of each pudding and refrigerate until chilled, at least 3 hours, or overnight.
In a chilled bowl, whip the remaining 3/4 cup of heavy cream with the remaining 1/2 teaspoon of vanilla until soft peaks form. Garnish the puddings with the whipped cream and toffee pieces and serve.
The recipe can be prepared through Step 2 and refrigerated for up to 2 days.