In a large saucepan combine the potatoes, peeled and cut into 1-1/2 to 2 inch pieces, and the garlic with enough salted cold water to cover the potatoes by 1/2 inch and simmer them, covered, for 15 to 25 minutes, or until they are tender but not falling apart. While the potatoes are cooking, in a small saucepan heat the cream with the butter, the goat cheese, and salt and pepper to taste over moderately low heat, stirring, until the butter and cheese are just melted and smooth and keep the mixture warm. Drain the potatoes and garlic and force them through a food mill fitted with the medium disk or a ricer into a bowl. With an electric mixer beat in the butter mixture, the scallion, and salt and pepper to taste, beating just until the potatoes are fluffy and smooth (do not over-beat), and transfer the mixture to a 1 quart shallow flameproof baking dish. The potatoes may be prepared up to this point 2 days in advance and kept covered and chilled. Reheat the potatoes in a preheated 300° F. oven for 20 minutes, or until they are heated through, before broiling them. Broil the potatoes under a preheated broiler about 4 inches from the heat for 3 to 5 minutes, or until the top is golden. Serves 4 to 6. pot 20