Melt 2 oz unsalted butter over medium low heat. Add 8 oz dark brown sugar and stir until the sugar looks like wet sand.
Cook on medium low, stirring occasionally, for about 5 minutes. The mixture will begin to liquify.
Slowly whisk in 1 cup of the cream. BE CAREFUL, the mixture will bubble up and steam when the liquids are added. Keep your face away from the pot.
Cook over low heat for about 10 minutes, whisking occasionally until the butterscotch becomes more viscous, very smooth and silky. Whisk in the remaining cream, 3/4 cup of the milk and2 tablespoons bourbon. Reduce the heat to low.
In a large bowl, whisk together the reserved 1/4 cup of milk and 1 oz corn starch, add 6 large egg yolks and ¼ teaspoon table salt.
Increase the heat under the butterscotch to medium high and bring it to a full boil. Whisk the butterscotch into the yolk mixture. Return the mixture to the pan.
Stirring constantly, cook over low heat until the pudding begins to thicken and just begins to simmer.
Immediately remove from the heat and pour the pudding through a sieve back into the mixing bowl. Whisk in 2 teaspoons vanilla extract
Divide the pudding among 6 serving dishes. Chill until set.
Notes
Use an additional 2 Tbsp of milk for alcohol-free version