How much evaporated milk do I use for a half a cup of milk
In order to substitute evaporated milk for regular milk, you need to reconstitute the milk according to package instructions. Usually, that's a 1 to 1 ratio. So you would use 1/4 cup each of evaporated milk and water. (double check the label, other concentrations may exist)

See: Can evaporated milk be converted to &quot;regular&quot; milk?