Melt butter in a large Dutch oven over medium-high heat. Add squash, potato, salt, and pepper to pan; sauté 3 minutes. Add leek; sauté 1 minute. Stir in broth; bring to a boil. Reduce heat, and simmer 20 minutes or until potato is tender, stirring occasionally. Place half of potato mixture in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until smooth. Pour into a large bowl. Repeat procedure with remaining potato mixture. Stir in half-and-half. Cover and keep warm.
Arrange bread slices in a single layer on a baking sheet; sprinkle evenly with cheese. Broil bread slices 2 minutes or until golden. Ladle 1 cup soup into each of 8 bowls; top each serving with about 1 teaspoon chives. Serve 2 bread slices with each serving. Garnish with freshly ground black pepper, if desired.
Wine note: This is one vegetable soup that can easily handle a lighter red wine. Stick with the French theme and look for bargains from Burgundy, like Louis Jadot Pinot Noir 2005 ($20). This wine has pretty red berry fruit, great balance, and gentle tannins that make it ideal for lower-fat dishes. The underlying earthy, leathery flavors bring out the rustic nuances of the potatoes and squash. —Jeffery Lindenmuth