Preheat your oven to 350°F (175°C).

Scrub the Yukon Gold potatoes and slice them into ⅛-inch rounds.

Melt butter in a medium saucepan over medium heat and sauté diced onions and minced garlic until soft.

Stir in all-purpose flour, then gradually add milk and chicken broth, stirring until thickened.

Remove from heat and stir in the cheddar, mozzarella, and parmesan until melted.

Layer one-third of the sliced potatoes, then pour one-third of the cheese sauce over them. Repeat twice more.

Cover the casserole dish with aluminum foil and bake for 30 minutes.

Uncover and bake for an additional 35-45 minutes until golden brown and fork-tender.

Let the dish cool for about 10 minutes before serving.