Preheat your oven to 400°F (200°C).

Melt butter in a saucepan over medium heat, add garlic and onions, sauté for about 5 minutes until softened.

Sprinkle flour, whisk in heavy cream and half-and-half, cook for 3-4 minutes until mixture thickens.

Stir in asiago cheese, rosemary, paprika, sage, salt, pepper, and nutmeg until mixed and melted.

Slice sweet potatoes into thin rounds, about ⅜ inch thick, for uniform cooking.

Grease a baking dish with butter, layer sweet potatoes, and pour sauce evenly over them.

Stir half of the Colby Jack and smoked gouda into the sauce and pour over potatoes, top with remaining cheeses.

Cover with aluminum foil and bake for 45-50 minutes until tender.

Remove foil, bake for an additional 15-20 minutes until top is golden brown and bubbling.

Let rest for 10-15 minutes before serving.