Creamy Potato & Leek Soup

INGREDIENTS

• 4 medium leeks, white and light-green parts halved lengthwise, washed, and sliced thin (about 4 cups), dark green parts halved, washed, and cut into 2-inch pieces
• 2 cups vegetable broth
• 2 cups water
• 4 tablespoons unsalted butter
• 1 cup chopped onion
• 1 teaspoon salt
• 1 small russet potato (about 6 ounces), peeled, halved lengthwise, and cut into 1/4-inch slices
• 1 bay leaf
• 1 (4-inch) sprig fresh thyme or tarragon
• 1 large slice white sandwich bread, lightly toasted and torn into 1/2-inch pieces
• Ground black pepper