Step 1

In a medium saucepan, whisk together the whole milk and corn starch until smooth.

Step 2

Place the saucepan over medium heat, stirring frequently to prevent the mixture from sticking to the bottom of the pan. Continue until the mixture begins to thicken slightly.

Step 3

Reduce the heat to low and add the egg yolk, whisking constantly to avoid curdling. This step helps to create a rich, creamy texture without the need for flour.

Step 4

Gradually add the cream cheese, stirring until fully melted and incorporated.

Step 5

Slowly add the shredded cheddar cheese, American cheese, and Parmesan cheese, stirring constantly until all the cheese melts and the sauce is smooth.

Step 6

If the sauce is too thick, add a little more milk to reach your desired consistency. If it's too thin, continue to cook on low heat, stirring frequently until it thickens.

Step 7

Taste and adjust seasoning if necessary.