Step 1

Gather all the ingredients.

Step 2

Rinse the leeks and cut in half lengthwise. Chop into 1” (2.5 cm) pieces.

Step 3

Carefully wash the leeks again in running water.

Step 4

Butter a baking dish.

Step 5

In a large skillet, heat the rest of the butter on medium-high heat and add leek.

Step 6

Cover and let simmer for 20 minutes. Stir occasionally and cook until leeks are soft.

Step 7

Meanwhile, peel and slice the potatoes into ¼” (1.3 cm) pieces.

Step 8

Soak in water until you are ready to use them (prevent from changing color).

Step 9

When the leeks are soft, add thyme, salt, pepper, and heavy whipping cream. Simmer another 5 minutes until the sauce gets thickened.

Step 10

Preheat the oven to 400°F (200ºC). Divide the potatoes, leek mixture, and each cheese according to your baking dish size. I divided them in half as my baking dish is shallow.

Step 11

Layer one portion of potatoes in the baking dish.

Step 12

Then layer one portion of the leek mixture.

Step 13

Layer one portion of each cheese. Repeat for each layer.

Step 14

Sprinkle panko and green onion on top. Cover with the aluminum foil and bake for 45 minutes. To check whether the dish is done, test by inserting a skewer through the foil. If the skewer is able to go through the potato smoothly then it’s ready. Remove the cover and change the oven setting to broil. Broil for 2-3 minutes until golden brown on top. Remove from the oven and let it sit another 15 minutes. Serve warm.

Step 15

You can keep the leftovers in an airtight container and store in the refrigerator for up to 3 days. The potato texture will change when frozen, so I do not recommend freezing this dish.