1. In a large saucepan, beat together eggs, sugar and salt.
2. Stir in just two cups of milk.
3. Cook over low heat, stirring constantly. Make sure to get in the corners of the pan or the eggs might curdle when they get hot.
4. When the mixture reaches 160 F or is thick enough to coat a spoon with a thin film, remove from the heat.
5. Mix together the bourbon and dark rum but the alcohol is optional.
6. Next stir in the remaining 2 cups milk and a vanilla.
7. Cover with plastic wrap and refrigerate until thoroughly chilled.