How to Make It
Melt the butter in a large skillet; pour off 2 tablespoons and set aside. Add the onions and a pinch of salt to the skillet and toss until evenly coated. Moisten a piece of crumpled parchment or wax paper and press it on the onions. Cover and cook over moderately low heat, stirring occasionally, until tender but not browned, about 15 minutes.
Meanwhile, bring a large saucepan of salted water to a boil. Add the parsley and blanch until wilted, about 1 minute. Drain and press the parsley dry, then transfer it to a blender. Add the reserved 2 tablespoons of melted butter, the stock and lemon juice and puree until smooth. Season with salt and pepper and transfer to a small saucepan.
Toast the curry powder in a small skillet over moderate heat until fragrant and lightly browned, about 30 seconds. Transfer to a plate.
Gently warm the parsley sauce and spoon it onto plates. Mound the onions in the center, sprinkle with the curry powder and serve.