Melt butter in a sauce pan over medium heat.

Once butter is melted, stir in the flour to form a silky roux and let cook for about a minute

Then add about ¼ cup of the milk and stir to incorporate everything so there are no “clumps”. Keep stirring while you slowly add in another ½ cup of the milk. And let cook for about a minute more.

Then add the rest of the milk and stir while it heats. Bring to a slow rolling boil as you stir. Let cook at a simmer for about a minute and then turn heat off, you will see it start to thicken.

Add the salt, pepper and parmigiano cheese and stir. Let thicken as it cools.