Potato Gratin

method

  1. Preheat the oven to 350 °F (180 °F). Grease a 9 x 13-inch (3 L) or other similarly sized casserole dish with butter.
  2. Melt the butter over medium heat in a medium saucepan and stir in the flour with a wooden spoon. Continue to cook, stirring continuously, for about 4 minutes until the mixture smells slightly nutty but does not change colour. Add the milk in 3 parts, beating well with a whisk and letting the mixture thicken before adding more milk. Whisk in the Dijon and garlic.
  3. Reduce the heat to medium-low and add the Cheddar and Swiss cheeses in 3 parts, whisking until the cheese has melted before adding more. Whisk in the parsley and vermouth and season to taste with salt and pepper. Keep the sauce warm over low heat.
  4. Cover the bottom of the casserole dish with a layer of sliced potatoes, overlapping them a little. Ladle about 1 cup (250 mL) of the cheese sauce overtop (it doesn’t have to cover the potatoes completely). Repeat the layering of potatoes and sauce about 6 times, finishing with a layer of the sauce. Place a piece of parchment over the dish (it can touch the sauce) and cover the dish with aluminum foil.
  5. Bake the gratin for about 1 hour, until a knife inserted in the centre yields easily. Remove the foil and parchment and increase the oven temperature to 400 °F (200 °C).
  6. Cook the gratin until the top is brown and bubbles, about 10 minutes. Let the potatoes cool for 15 minutes before serving.

Make Ahead
You can assemble and bake this dish (without browning the top) and store it, covered with plastic or parchment (not foil), in the fridge for up to 1 day. To re-warm, place the gratin in the oven, covered, for 40 minutes at 300 °F (150 °C) and then uncovered for 10 minutes at 400 °F (200 °C).

Recipe from Set for the Holidays with Anna Olson, Appetite by Random House, 2018