Chorizo and Potato Spanish Tortilla Bites

Put oven rack in middle position and preheat oven to 400°F. Lightly oil a 13- by 9-inch baking pan or dish.

Finely chop white and green parts of scallions and reserve separately.

Heat oil in a 12-inch heavy skillet over moderately high heat until hot but not smoking, then cook onions, garlic, white parts of scallions, 3/4 teaspoon salt, and 1/4 teaspoon pepper, stirring occasionally, until onions are golden, about 6 minutes. Add chorizo and cook, stirring occasionally, until just beginning to brown and release oil, about 4 minutes. Reduce heat to moderate, then stir in potatoes and cover skillet. Cook, stirring occasionally, until potatoes are tender, about 10 minutes. Transfer mixture to a large bowl and cool slightly.

Whisk together eggs, sour cream, cheese, scallion greens, and remaining 1/2 teaspoon salt and 1/4 teaspoon pepper in a bowl, then pour into baking pan. Sprinkle potato mixture over eggs (some potatoes will stick out). Bake until custard is set, about 20 minutes. Cool in pan on a rack to warm or room temperature. Trim 1/2 inch off each side, then cut tortilla into 1 1/2- by 1-inch rectangles.