Step 1

Place a rack in the center of your oven and preheat to 350°F.

Step 2

Melt 1 tablespoon butter in a 10- or 12-inch oven-safe skillet* over medium heat. Add the panko and cook, stirring, until the panko is crisp and golden, about 3 minutes. Stir in the garlic powder and ¼ teaspoon salt. Transfer to a small bowl.

Step 3

Melt the remaining 2 tablespoons butter in the same skillet over medium heat. Add the flour and stir for 2 minutes, until thick and pasty. While whisking, slowly add the milk, breaking up any lumps. Add the garlic, nutmeg, remaining ½ teaspoon salt, and the pepper. Bring to a simmer, reduce the heat to low, and continue to whisk until the mixture is thick, about 6 minutes.

Step 4

Add the spinach and cook, breaking it up with a spoon and stirring to incorporate, until warmed through, about 4 minutes.

Step 5

Add the parmesan and cream cheese and cook, stirring well, until fully melted and incorporated.

Step 6

If using an oven-safe skillet, top with the panko. Bake until the spinach casserole is golden brown, 10 to 15 minutes. Sprinkle with chives and let cool for 10 minutes in the pan before serving.