This has to be a favourite of many vapers.
A bit of milk flavour instantly makes any e-liquid taste fuller, richer, and sweeter. It works perfectly in so many flavour profiles.
Milk is an essential component of milkshake and ice cream e-liquids, but it's also great in a fruity e-liquid or any e-liquid with a cake or doughnut flavour.
In the case of milk, extra sweetness can badly impact the e-liquid. If you really want to taste milk flavour in its purest form, go for an e-liquid that's sweet but not excessively sweet.