1. Place potatoes in a large saucepan of cold salted water. Bring water to a boil. Reduce to a simmer, and cook until potatoes are fork-tender, about 20 minutes. Warm milk in a small saucepan. Drain potatoes, and return to the pan. Add warm milk, butter, salt, and pepper.

2. Mash the mixture with a potato masher until all the liquid is incorporated and the butter has melted. Transfer mixture to a metal mixing bowl. Cover with aluminum foil; set over double boiler to keep warm.

3. Meanwhile, heat olive oil in a large skillet on medium heat. Add onions, and saute stirring often, until golden brown, 10 to 12 minutes.

4. Adjust the seasoning of potatoes with salt and pepper, if desired. Transfer the potatoes to a serving dish. Spoon the onions over the potatoes, and crumble Roquefort cheese over the top. Serve immediately.