"Laxpudding," a classic Swedish dish of potatoes and gravlax (cured salmon), is pure home cooking that's still elegant enough for any holiday table. Aquavit chef Emma Bengtsson sticks to tradition by bringing the potatoes and gravlax together with a rich egg custard and lots of fresh dill.
Preheat oven to 350 F. Peel and slice potatoes, about ¼ inch thick. Peel and thinly slice the onion. Grease the baking dish with 1 tablespoon butter. Layer the potatoes across the bottom; add a layer of onions, followed by a layer of gravlax. Repeat with one more layer each of potato, onion, and gravlax; finish with a layer of potato, then a final layer of onion. (Note: Based on the exact size and shape of your baking dish, you may have extra ingredients. Use the remainder to make a second, smaller gratin, or reserve the ingredients for another use.)
Crack eggs into a bowl; add the milk, then whisk to combine. Add white pepper and salt, and stir to combine. Pour over the casserole dish, just to cover the top, distributing evenly. Finely chop ¾ of the dill; sprinkle over the top of the casserole. Bake in the oven until potatoes are cooked through and the top is golden brown, 40–45 minutes.
Test potatoes for doneness by inserting a knife through the layers of the gratin. It should slide in smoothly and come out clean. Allow to rest for about 10–15 minutes.
Meanwhile, melt remaining butter in a small skillet. Plate the gratin, and top each serving with a dill sprig and a generous drizzle of melted butter. Serve with fresh lemon wedges.