Salmon Potato Gratin

1. Gather all the ingredients. You will need one 8- x 8-inch (20- x 20-cm) baking dish.
2. Preheat the oven to 350°F (177ºC) and set an oven rack in the middle position. Combine ½ cup whole milk and 1½ cups heavy (whipping) cream. Grease an 8-inch (or 2-quart) baking dish with butter.
3. Peel 3 russet potatoes and cut them into ⅛-inch (3-mm) uniform slices. Some people like to use a mandoline slicer and get very thin slices. I personally like them to be slightly thicker. Tip: If you are making ahead, soak the potatoes in water for 10 minutes to prevent them from changing colors.
4. In a large mixing bowl, add the potatoes, 1 tsp Diamond Crystal kosher salt, ¼ tsp freshly ground black pepper, and ¼ tsp dried thyme.
5. Toss everything until evenly coated. Arrange some of the potato slices in a single layer, overlapping slightly, on the bottom of the baking dish. This baking dish is shallower than other baking dishes I have. Therefore, I made 2 sets of layers and used half of the ingredients for each layer. You may be able to make 2–3 layers.
6. Evenly distribute half of 1⅓ cups Homemade Salmon Flakes over the potatoes, then sprinkle half of the 1 cup Parmigiano-Reggiano or Parmesan cheese on top.
7. Pour half of the cream mixture over top. Repeat with remaining potatoes and Salmon Flakes.
8. Sprinkle the remaining cheese and cream.
9. Sprinkle a generous amount of 2 Tbsp panko over the top.
10. Place in the oven and bake, uncovered, for about an hour, or until the potatoes are tender and golden on top.
11. Check the doneness by inserting a skewer. If you prefer a nice char on top, turn the broiler on High for 1 to 2 minutes. Keep an eye on the baking dish so the top won’t get burnt. Remove the baking sheet from the oven and set aside for 10 minutes before serving. Sprinkle with fresh thyme, if using, and then serve.

Doubling the Recipe

1. For the potatoes to cook more evenly, I recommend making 2 baking dishes rather than 1 large baking dish.