In a mixing bowl combine the egg, egg yolks, and cornstarch. Whisk in 1/2 cup of milk and set aside. Combine the rest of the milk and the heavy cream and milk and set aside.

In a large, heavy-bottomed sauce pan over medium-high heat, mix brown sugar, ½ cup water, and the salt and stir to combine. Cook until the water has evaporated and the liquid is molten, dark brown, and smells caramelized, 10 to 12 minutes.

Whisk in the cream and milk mixture you will have a vigorous reaction and the sugar may seize, this is ok just keep whisking and it will melt into the milk. Bring the mixture to a boil, then reduce the heat to medium.

Add 1 cup of the butterscotch mixture to the egg mixture whisking constantly. Pour the egg mixture back into the rest of the butterscotch mixture and whisk continuously. Bring to a boil and whisk until the custard is very thick, about 2 minutes.

Remove from the heat and whisk in the butter and bourbon.

Strain the custard through a fine mesh strainer to remove any lumps, and divide among eight 8-ounce jars. Cover with plastic wrap or lid and refrigerate until completely chilled. Top each budino with 1 tablespoon of the warm caramel sauce.

Garnish with additional toppings such as whipped cream, Maldon salt, espresso powder, pistachios, or crushed chocolate graham crackers.