5 medium red-skinned potatoes (about 1 3/4 pounds)
2 tablespoons unsalted butter
2 tablespoons canola oil
1 red bell pepper, cut into 3/4-inch pieces
1 large onion, cut into 3/4-inch pieces
1/4 teaspoon cayenne pepper
1/4 teaspoon pure mild chile powder
1/4 teaspoon sweet paprika
1/4 teaspoon celery seeds
Steam the potatoes over boiling water until almost cooked through, about 15 minutes. Let the potatoes cool, then cut them into 1-inch chunks.
In a large cast-iron skillet, melt the butter in the oil until foamy. Add the red bell pepper and onion and cook over moderately high heat until just softened, about 5 minutes. Stir in the potatoes, then cook over moderate heat without stirring until golden and crusty on the bottom, about 5 minutes. Turn the potatoes and cook, turning occasionally, until golden all over, about 15 minutes longer. Stir in the cayenne, chile powder, paprika, celery seeds and a generous pinch of salt and serve immediately.