Mashed Potato Casserole

In a medium saucepan over medium heat, bring milk, thyme, bay leaves, 4 tablespoons butter, 1/2 teaspoon salt, and 1/4 teaspoon pepper to a simmer. Remove from heat, cover, and let stand 1 hour.

Preheat oven to 375°. Grease a 2 1/2- to 3-quart baking dish with butter.

In a large pot, combine potatoes and garlic. Cover with at least 2" water; season with 2 tablespoons salt. Bring to a boil and cook until fork-tender, 12 to 15 minutes. Reserve 3/4 cup cooking liquid, then drain. Return potatoes and garlic to pot and mash with a potato masher until smooth.

Meanwhile, return infused milk to a bare simmer over medium heat; discard thyme and bay leaves. Add cream cheese and 1/4 cup Parmesan and stir until smooth and melted. Add to mashed potatoes along with eggs. If needed, gradually add reserved cooking liquid until consistency is thick but spreadable; season with salt and pepper. Transfer mixture to prepared dish.

In a small skillet over medium heat, melt remaining 2 tablespoons butter. Cook, swirling pan, until butter begins to brown and smell nutty, 2 to 3 minutes. Remove from heat and stir in panko and remaining 1/4 cup Parmesan; season with salt and pepper. Sprinkle over mashed potato mixture. Cover pan with foil.

Bake casserole 10 minutes. Uncover and continue to bake until hot and topping is golden brown, 20 to 22 minutes. Top with chives.