In a saucepan, combine the sugar, cornstarch, cocoa and salt. Whisk in the milk. Bring to a boil over medium-high heat, whisking constantly. Boil for 1 minute.

In another bowl, whisk the egg yolks. While whisking the yolks constantly, add in about a cup of the hot milk mixture. Pour the mixture back into the pan, whisking constantly. Stir until thickened, about 1 minute. Remove from the heat and stir in the butter and vanilla. Pour into a large bowl and cover with plastic wrap, pressing the wrap onto the surface of the pudding.

Refrigerate the pudding until set up, at least 2 hours. Before serving, stir in 1 1/2 cups of the chopped candy bars, then divide the pudding between 5 serving bowls. Top with the remaining candy bars. Top with whipped cream, if desired.

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Adapted from All You October 21, 2011