- In a saucepan of salted water, cook the potatoes until tender. Drain. With a masher, coarsely crush the potatoes with the butter. With an electric mixer, purée the potato mixture with the milk until smooth. Add milk, if needed. Adjust the seasoning. Set aside in a pastry bag fitted with a large fluted tip.
- With the rack in the middle position, preheat the oven to 220 °C (450 °F).
- In a saucepan, soften the shallots in the butter. Add the flour and cook for 1 minute while stirring. Add the milk and wine and bring to a boil, stirring with a whisk. Cook for 1 minute. Remove from the heat. Season with salt and pepper. Add the scallops and 125 ml (1/2 cup) of the cheese. Divide the filling into four scallop shells or four small gratin dishes. Garnish the rim with the mashed potatoes. Sprinkle with the remaining cheese. Bake for about 25 minutes or until nicely browned.
- Serve with a mesclun salad.
You can freeze the St. Jacques shells before baking.