Step 1

Preheat oven to 250°. Place potato and 1 Tbsp. Diamond Crystal or 2 tsp. Morton kosher salt in a medium pot; pour in cold water to cover. Bring to a boil over medium-high heat, then reduce heat to medium and simmer until potato is fork-tender, 25–30 minutes total. Remove potato from pot; let cool slightly.

Step 2

Meanwhile, return water in pot to a boil. Add leeks and cook until very soft, about 5 minutes. Drain well.

Step 3

Using your hands, remove skin from potato; discard. Coarsely chop flesh. Transfer to a food processor and add leeks; pulse until chunky and well combined (it shouldn’t be homogeneous and smooth). Transfer mixture to a bowl. Add almond flour, breadcrumbs, cumin, and 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, season with pepper, and mix well.

Step 4

Pour oil into a medium heavy skillet, preferably cast iron, to come ¼" up the sides; heat over medium-high. Working in batches of 3 or 4 and using a ¼-cup measure, scoop potato mixture into your hands and flatten into thin 3"-diameter disks. (Mixture may feel soft, but it will hold together.) Fry latkes, reducing heat if browning too quickly, until deep golden brown, about 4 minutes per side. Transfer to a wire rack set inside a rimmed baking sheet; season with salt. Keep warm in oven while you make remaining latkes. Serve with tzatziki.