Preheat oven to 400°F (200°C).

Grease a 13x9 inch baking dish.

Quarter the red potatoes and place them in the greased baking dish.

Bake the potatoes, uncovered, for 40 minutes.

While the potatoes are baking, melt butter in a small saucepan over medium heat.

Stir in flour until smooth.

Gradually add milk, stirring constantly to avoid lumps.

Bring the mixture to a boil, then reduce heat and simmer for 2 minutes, stirring constantly, until thickened.

Stir in the grated Parmesan cheese, minced fresh rosemary, minced garlic, salt, and pepper.

Pour the sauce over the baked potatoes, stirring to coat evenly.

Return the baking dish to the oven and bake for an additional 8-12 minutes, or until the sauce is bubbly and the potatoes are tender.

Serve hot.