Step 1

Place potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain and return to pot.

Step 2

Preheat the oven to 375 degrees F (190 degrees C). Grease a glass baking dish.

Step 3

Combine milk, cream cheese, 1/3 cup green onions, egg, butter, garlic, and salt in a bowl. Pour onto the prepared potatoes. Mash together until mixture is smooth. Spoon into the prepared baking dish. Sprinkle with Cheddar cheese and remaining green onions.

Step 4

Bake in the preheated oven until lightly browned, about 40 minutes.