I just watched a commercial for Idaho potatoes that said they're special because they're especially 'dense'. When I was in Spain my señora told me that when she came to American she couldn't make proper potato omelette because the potatoes didn't act right. Does anyone know enough about potatoes to know if potatoes in America are any different than the ones you would find in central Spain?
What are sometimes referred to as Idaho potatoes are generally russet potatoes, a variety of mealy potato commonly grown in Idaho. Mealy potatoes are one of the two broad categories of potatoes: Waxy and Mealy. Mealy potatoes are more dense, higher in starch and lower in sugar and moisture than waxy varieties. Mealy potatoes are used in dishes such as baked potatoes, mashed potatoes, and french fries as they maintain a lighter, mealy texture and don't brown too quickly.
Waxy potatoes include most red skinned potatoes and are less dense with less starch and more sugar and moisture. Waxy potatoes maintain their shape better when boiled so are preferred for that preparation method as well as sauteing and roasting.
Some potatoes exist near the middle of these two extremes and are sometimes referred to as all-purpose potatoes as they will work in a wide variety of preparations. Yukon Golds are probably the most widely available example of all-purpose / medium density potatoes in the US.
There are a huge variety of potatoes grown throughout the world. The trick is to figure out if your senora's recipe requires mealy or waxy potatoes and then purchase the a variety from that category. If you don't know whether the variety in question is mealy or waxy you can check by placing the potato in a brine made of 1 part salt to 11 parts water. If the potato floats it is waxy, if it sinks it is mealy.
Potatoes first came to Spain via Peru in the 16th century. Conquistadors brought potatoes back to Spain since they didn't find the gold in Peru they were looking for. Well, Peru has a very, very long history with the potato and more varieties are found there than anywhere else in the world.Potatoes of Peru This link highlights some of the varieties of potato that are in common use in Spain today: Potatoes of Spain
The history of potatoes in The United States is somewhat shorter, one variety was originally thought to be native to the east coast of North America, but it too was actually brought to North America from South America. Potatoes in the US really took off when Scottish and Irish immigrants started to plant their potatoes. Guess the origin of Scottish and Irish potatoes? You guessed it, South America around Peru.
What is the point of this history lesson? It's simple. Potatoes everywhere have the same origin, and therefor similar characteristics. Spain and the United States both have many varieties of potato, unquestionably any potato known to Spain can be successfully substituted with an American potato (and vice versa). The trick is knowing the characteristics of the potato you know, and finding a variety in the other part of the world that shares those characteristics. Level of waxiness is probably the most important characteristic to try to match. The variety and age of the potato determines it's waxiness. Here's a link to get you started. Characteristics of Common Potatoes. Respond here with a comment including more about your señora's preferred potato, and I'll help you find a match.