Preheat your smoker to 250°F (or preheat the oven if skipping the smoking step).

Brown the ground beef in a large cast iron pan. Season with salt and pepper, then remove and set aside.

Add 1 tablespoon of butter to the same pan, sauté the diced onion until translucent, then stir in the minced garlic for 30 seconds.

Push the onion-garlic mixture aside, melt the remaining butter, and whisk in the flour. Slowly add milk, whisking until smooth and lump-free.

Stir in the shredded Gouda cheese, Greek yogurt, and oregano. Mix until the cheese is fully melted and smooth. Return the cooked ground beef to the mixture.

Butter a 9x13 baking dish or cast iron pan. Layer a third of the sliced potatoes at the bottom and season with salt. Add half of the beef mixture on top. Repeat with another layer of potatoes, the remaining beef, and end with a final potato layer.

Combine breadcrumbs, Parmesan, and olive oil. Sprinkle evenly over the top layer of potatoes.

If using a smoker: Place the casserole in the smoker and cook for 1–1.5 hours until the potatoes are tender and the topping is golden brown.

If using an oven: Preheat to 350°F. Cover the dish with aluminum foil and bake for 30 minutes. Remove the foil, increase the temperature to 400°F, and bake for an additional 30 minutes until golden.