If the corn is frozen, allow it to defrost. If its fresh, cut it off the cob and set it to the side.
Heat butter in a saucepan over medium-low heat. When the butter is melted and starting to bubble, pour the flour into the pan and whisk it in with the butter until a paste forms.
Reduce the heat to low and slowly whisk in the heavy cream making sure to whisk out any lumps. Whisk in the milk and the salt keeping the mixture smooth.
Stir the corn kernels and the grated parmesan into the pot. Increase the heat to medium until the mixture simmers. Reduce the heat again and allow it to simmer for 15 minutes, stirring occasionally.
Remove from heat and serve with fresh herbs like parsley or thyme.
Notes
I find that sweet corn gives this a better flavor
You can use canned corn, but I prefer fresh or frozen