Add whole milk to a small-medium sauce pan.
Bring the milk to a simmer over medium heat.
Once it has started to simmer, lower the heat and continue to simmer for about 25-30 minutes.
Gently stir to keep the milk from scorching on the bottom of the pan.
After simmering, the milk should be reduced by a little over half... leaving you with one cup of homemade evaporated milk.