Frites (pronounced without the "s") is what French people call julienne-cut strips of potato deep-fried in oil and eaten hot. Depending on where you live, you may call them french fries or chips. They seem to have become a universal food, at least in the Western World.
In France, as you can imagine, they are very popular. They are also popular in Belgium, perhaps even more so than in France. I am not sure if the idea for this dish originated in France or in Belgium. In France it is eaten mainly in the northern part of the country, such as the Département of Brittany.
Like most French family cooking, it is a very simple dish. If you are going to try it, make it exactly as described below. After that, if you want to personalize it, feel free to do so. But please do not call it "salad and frites" if you change it drastically.
Make a very simple salad of greens only. It is best to choose loose leaf greens instead of greens in a tight head. Romaine, endive, arugula and radicchio are good choices. You can also use mixed greens if you wish but please stay with just greens - no onion, tomato, celery, green pepper or anything else - that is a salade mixé and not a salade.
Make sure your greens are washed and dried. I like to use a salad spinner. It is amazing how much water is removed using this gadget, and the leaves are not bruised as they could be if patted dry. Wrap the greens loosely in a clean white cotton towel to let them dry further while you make the dressing.
The only possible dressing for this dish is a vinaigrette, a basic oil and vinegar dressing. Better cooks than me have already noded the recipe (see sneff's in the node, salad). It is best to stay with a neutral oil - if you are going to use an olive oil, do not use a "fruity" or flavored one. For the vinegar, Balmasic or a red wine vinegar are preferred.
Follow any recipe for french fries or chips, or buy them from a fast food establishment. The important thing is that they are hot.
How to serve and eat this dish
Put the dried greens in a large bowl, drizzle with the dressing, toss well. Serve the frites in a separate bowl at the same time. The salad goes on your plate first, then a serving of frites directly on top of the salad. Using your knife and fork, cut a forkful of salad and frites and enjoy.
The vinegar enhances the flavor of the frites. The heat of the frites has an effect on the greens so they are a bit like the "wilted salad" found in Pennsylvania Dutch cuisine. You can also serve thin slices of ham with this dish. In France, where the main meal on a Sunday is always served at noon, jambon avec salade et frites is often served for Sunday night supper.