Preheat oven to 400 degrees F. On a sheet tray, gently toss pretzels, butter and 2 tablespoons sugar. Bake until sugar melts and crystallizes on the pretzels, about 10 minutes.
Meanwhile, in a medium saucepan, whisk together the cocoa, 1/2 cup sugar and cornstarch. Form a well in the center and slowly whisk in milk over medium heat. This helps prevent the cornstarch from clumping. Bring mixture to a boil to thicken. Remove from heat. In a small bowl, whisk a little of the milk mixture into the egg to temper. Add egg mixture to the pot of milk. Heat over low until mixture thickens to a pudding-like consistency, about 3 to 5 minutes. Mix in chips until melted and combined well. Pour pudding into ramekins. Chill at least 1 hour. To serve, top with pretzels.