Whisk the whole milk and heavy cream together. Set aside. Whisk the egg yolks and cornstarch together. Set that aside too. Have both ready to go in step 3.

Whisk the brown sugar, water, and salt together in a medium heavy duty saucepan over medium heat. Without stirring, allow to cook and bubble until darker brown, about 5-6 minutes. It should begin to smell caramelized at that point. If desired, you can take the temperature with a candy thermometer to be certain it is ready. Look for around 240°F (116°C).

Slowly and carefully whisk in the heavy cream/milk. It will sizzle and may splatter, so pour in slowly. Cook on medium heat until mixture begins to boil. Once boiling, remove about 1/2 cup of the mixture and, in a slow and steady stream, whisk into the egg yolks. Keep those egg yolks moving so they don’t scramble. In a slow and steady stream, pour and whisk the egg yolk mixture into the pot.

Turn the heat down to low. The pudding will immediately begin to bubble and thicken. Whisk and cook for 1 minute. Remove from heat and stir in the butter until completely smooth, then add the vanilla and bourbon.

Cool for 5 minutes, then pour into serving glasses or bowls. Cover tightly with plastic wrap directly on the surface of the pudding (to prevent a skin from forming) and refrigerate for 4-6 hours or overnight until chilled and thickened.

Serve with optional toppings. Cover and store leftovers in the refrigerator for up to 4 days.