The idea is always simple - like with padrón peppers. These peppers are served all over the place in tapas bars when they're in season. They are fried in olive oil until slightly charred, then sprinkled in salt. That's it. Sounds incredibly simple; and it is. But, crucially, what makes them so delicious in the tapas bars is that they are just the right peppers grown in just the right soils in Galicia. They are fried in high quality olive oil and sprinkled with high quality coarse salt. You have to put all these elements together to make padrón peppers just right.
The patatas a la riojana we had that day were incredible. What, we asked, is the key to making something seemingly so simple so good? The matriarch of the place gladly explained how to make dish to us. According to her, there are two key things. One is in the ingredients: to make it just right, you need to use chorizo that hasn't completely finished curing. This way, the chorizo releases more of its flavor into the dish (this, clearly, cannot be reproduced at home, unless you're curing your own chorizo) The second crucial thing is in the cutting of the potatoes: they need to be cut into little irregular pieces in a technique called cascar. This verb translates roughly to "crack" or "chip." The idea is that instead of cutting through the potato, you stick a pairing knife into it, then pull back so the potato breaks naturally where it wants and creates irregularly shaped pieces.
This affects the starch structure of the potatoes and has two effects. The first is that the starch from the potatoes thickens the sauce properly, and the second is that the potatoes more readily absorb the flavors of the sauce. If anyone knows a more detailed scientific explanation for this, please hit up the comments, I'd love to hear it... Looking around, I can hardly find any information on this cutting technique. The best I could find was this.
I find it fascinating, and I wonder why it's not better known.
And beyond stews and saucy dishes, I've found that cutting potatoes this way is great for frying too. In fact, a few Spanish sources insist that this is the proper way to cut potatoes for a tortilla de patatas, a statement with which I will not disagree. The potatoes seem to develop a beautiful golden color and that comforting creamy texture inside far more readily. Again, any information on why this is would be appreciated.
So try cutting your potatoes like this next time, whether it's for a stew, a tortilla, a breakfast hash, or any number of other dishes. Take a starchy potato and peel it. Using a pairing knife, hold the potato in one hand, insert the knife, then pull it back and upwards towards you. You will feel the potato break and crack. With a little practice, it goes very fast, and I find it much more fun than regular potato cutting.