Peel and slice potatoes into 1 inch cubes. Place into a large saucepan and cover with cold water, making sure water is at least 1 inch above the potatoes. Add salt to the water. Heat over medium high heat, stirring occasionally, until potatoes are fork tender. Drain potatoes.

In the same warm saucepan, add butter and half and half and stir well until melted. If necessary, turn heat to low and stir constantly until butter is melted. Add potatoes to the pan and mash. Stir in cheese, season with salt and pepper.

Grease a 2 1/2 quart baking dish with nonstick cooking spray and spread mashed potatoes into the baking dish. Set aside.

Peel gratin potatoes and slice potato lengthwise and then into 1/8 inch half moons. Add potatoes to a bowl and mix with melted butter, garlic, and half of the Parmesan cheese. Season with salt and pepper. Mix well.

Place potato slices, cut side down, on top of the mashed potatoes, layering them in the pan.

Cover with foil and bake at 400 degrees for 20 minutes. Remove from oven and discard foil. Add remaining reserved Parmesan cheese and return to the oven for 40 minutes.

Remove from oven and let stand for 10 minutes before serving topped with chopped fresh chives.