Deeply flavorful yet not too rich, these gratins make a delicious appetizer. But you can also serve them, with a couple of side vegetables, as a main course for a dinner party or a holiday meal.
Note: Although they’re best eaten the day they are made, the gratins can be baked for 40 minutes until just golden, then cooled and refrigerated up to 1 day. To serve, bring to room temperature and bake at 375 degrees for 6-8 minutes until bubbling at the sides.
*Note: If you prefer to make a large gratin rather than individual ones, use a medium-sized ceramic or glass baking dish. Layer the ingredients exactly as described above and bake at 375 degrees for 45-50 minutes.
Place the herbs and the garlic in the bowl of a food processor and pulse until chopped very finely. Or, place the herbs and garlic on a cutting board and chop finely. Set aside.
Heat a large nonstick skillet over high heat. Add the butter and oil. As soon as the butter is melted, add the mushrooms. Toss well and sauté for 6-8 minutes until golden, stirring only occasionally. Add the shallots and continue to sauté for 2 minutes until the shallots have softened. Add the herb-garlic mixture, salt, and pepper and continue to sauté for 30 seconds. Remove from heat and transfer to a bowl to cool slightly.
Preheat the oven to 375 degrees.
Whisk the milk, cream, salt, and pepper in a small bowl and set aside. Place 1/3 of the potato slices at the bottom of each ramekin*, enough to cover the surface. Top with ½ of the mushrooms. Then top with 1/3 of the potato slices. Top again with ½ of the mushrooms and finish with the remaining potato slices. Drizzle with the milk mixture. Sprinkle with the grated cheese. Bake for 45-50 minutes until golden and bubbly. Remove from the oven and let cool for 5 minutes before serving. Serve the gratins in their molds.