Thoroughly clean all equipment and surfaces.
Heat the milk to 140F (60C).
Dissolve the citric acid in 1/4 cup cool water. Add the citric acid and water combination to the milk and combine well. The cheese will begin to separate.
Let it sit for 10 minutes. At this point you should see clearly the separation of yellow whey and white cheese. If you do not see this separation, mix 1 tsp of citric acid in 1/4 cup cool water and slowly add it into the pot. Add only as much as needed to see the separation of whey from curds.
Once you have a clear separation, use a slotted spoon to scoop the cheese into a whey-moistened, cloth lined colander. Set aside to continue draining.
Over medium heat, melt the butter in a saucepan.
Add the salt, prepared drained cheese, reserved milk and shredded cheddar to the pot with the melted butter and stir over medium heat until melted and smooth, about 5 minutes.
Pour the mixture into a container and refrigerate for up to one week. It will be a thick liquid when warm but will harden into a soft, spreadable cheese as it cools.
