This is really not hard to cook - basically, you just fry up some potatoes - but there's a thing or two you need to know before you can talk about rösti with Swiss people.

First of all, please don't call it the Swiss national dish. It's associated with the German-speaking part of the country, to the point that our main "competitors" the French-speaking Swiss are far less keen on it. The dividing line between the language regions is known as the "Rösti Ditch" and any Swiss-German politician talking about things like teaching English instead of French as the first foreign language will be accused of "digging the ditch".

It's pronounced r-uhhh-sti, with a long vowel, not "rusty".

In restaurants outside of Switzerland you might see it as a side, like chips. In Switzerland, it's a main dish and often fills your whole plate. It's not meant to be a fancy meal, it's what a farmer would eat in the evening after a long day's work, and it's among other things a way to use up left-over potatoes just like the English bubble&squeak - in fact, one Swiss recipe book I have describes the main ingredient as "left-over potatoes from yesterday evening"!

There are different variations associated with different cantons of Switzerland, for example:

Bern - with bacon
Zurich - with onions
Wallis - with tomato slices and raclette cheese
Appenzell - with Appenzeller cheese and herbs

Rösti with a fried egg on top is also popular throughout the German-speaking part of Switzerland.