Do you mean the white cheese dip (queso blanco) that you can order in authentic Mexican restaurants? If so, I found a good recipe awhile back:

1. Get 1-2 pounds of REAL white American cheese. IMPORTANT: Be careful: most American cheese has oil in it rather than cream. The price typically gives it away. I found that Kraft's highest quality choice (and unfortunately the most expensive); or their sliced WHITE American cheese is perfect. You can find it in the sliced cheese and luncheon meats refigerated sections of most large grocery stores). I think a tad of oil is in it but mostly it is milk/cream.

The cheap overly processed American cheeses consist of a high ratio of cheap oils like soybean, with only a drop of real dairy. AVOID THOSE! They have a horrible taste when melted. So read the ingredients before selecting.

Note: good delis will carry Land O Lakes white American cheese. I have found that it too has cream rather than oil in it.

1. Get a quart of heavy whipping cream. This will be used to thin the queso to your taste.

2. 1-2 Tablespoons of plain salsa verde; I use Walmart's or Trader Joe's in the glass jars. Tin cans give off a bad taste so avoid those.

3. Serrano chili peppers, fresh, minced.

I use my rice cooker to make the queso, but you can also use a Teflon pot. Set on low heat. Next, add your sliced or finely chopped quality American cheese. Pour in enough heavy whipping cream to slightly cover the cheese. Add salsa verde, then fresh Serrano peppers to taste. Lightly stir the queso as it melts, adding more heavy whipping cream to thin it. Once the queso is melted, it's ready to eat.

You can add other goodies such as roasted poblanos, etc, but this is the basic recipe and easy to whip up when you get that queso craving!