½ to 1 tsp crushed red pepper, based on your heat tolerance
Kosher salt, to taste
For the yogurt sauce: combine the ingredients in a small bowl. Taste for seasoning, and add salt to taste. Cover and refrigerate until ready (I’d suggest making this ahead of time so the flavors can mingle).
For the potatoes: In a large saucepan, cover the potatoes with water, and add the 2tbsp of salt. Bring to a boil, and cook until the potatoes are very soft, and pierce easily.
Drain the potatoes, and transfer them to a baking sheet. Use the bottom of a measuring cup to flatten each potato to equal thickness, about 1/2 an inch each.
Over medium-high heat, heat the oil in a large skillet and fry the onions, stirring often, until brown and crispy (but don’t let them burn!). Remove to a small plate lined with a paper towel, and set aside.
Sprinkle the curry powder into the remaining oil and give it a stir, then carefully lay the smashed potatoes in the pan. Let them cook undisturbed until browned and crunchy, then flip and repeat to brown the other side, about 4 minutes on each side. Remove the cooked potatoes to a plate lined with crumpled paper towels and sprinkle with a few pinches of salt. Fry the potatoes in batches if necessary.
To serve, sprinkle the fried onions over the potatoes, and serve with the yogurt sauce.