5 tablespoons butter, unsalted, melted, divided
1⁄2 teaspoon caraway seeds
2 tablespoons duck fat, melted
1 teaspoon kosher salt
1⁄2 teaspoon freshly ground black pepper
2 pounds medium Yukon Gold potatoes, unpeeled, cut into 1⁄8” slices with mandolin
1 small sweet onion, halved and very thinly sliced
Maldon sea salt to finish
Put caraway seeds in a small dry skillet and place in the mouth of the oven. Toast for 30 to 45 seconds, shaking pan occasionally. Transfer seeds to a mortar and pestle and crush.
Brush a foil lined baking sheet with butter; set a 9” spring form ring on top.
In a large bowl add the caraway seeds, duck fat, 2 tablespoons of the butter, kosher salt and pepper. Add potatoes, toss to coat.
Arrange 1/4 of potatoes in an even layer inside ring on baking sheet, overlapping as needed. Toss onion in a large bowl with 1 tablespoon butter. Arrange 1⁄3 of onion over potatoes. Repeat layers twice more, finishing with a layer of potatoes. Carefully remove the ring.
Place in oven away from flame if possible and cook for 10 minutes. Spray a piece of foil with nonstick cooking spray and lay it over the top of the galette. If it is getting too brown, cover it before the 10 minutes are up. Continue to cook for about another 20 minutes, rotating the pan, until the potatoes are tender. Use a small paring knife to test for doneness.
Remove the foil and brush the galette with the remaining butter. Continue to cook for another 5 minutes, rotating the pan until the galette is a deep golden brown.
Run a thin spatula under galette to loosen from foil. Slide onto a platter, season with the Maldon salt if desired.