Preheat oven to 425 degrees F.
Slice one thin layer, lengthwise, off the bottom of each potato to allow them to lay flat.
Place a potato cut side down and use a sharp knife to make slices that are about 1/8 inch apart, slicing into the potato but not through it. The slices should stay connected at the bottom.
Carefully fan out the sliced pieces without breaking them apart. Repeat with each potato.
In a small mixing bowl, combine the melted butter, mustard, 3 Tbsp of the chives, and garlic. Set aside.
Using a pastry brush, brush the bottom of a large oven-safe skillet with the mustard butter.
Place the potatoes in the skillet and brush the outside and inside of each potato with the butter mixture. Be generous.
Sprinkle each potato with salt and pepper to taste.
Bake potatoes for about one hour, until tender on the inside and golden on the outside.
When cooked through, sprinkle with the remaining tablespoon of chives and serve.