1/4 cup olive oil
2 medium leeks, trimmed (leaving most of the green), split, washed, and sliced
12-15 garlic cloves
7 cups homemade chicken stock or low-salt canned chicken broth
2 pounds potatoes, peeled and cut into 1-inch cubes (about 4 cups)
1 teaspoon salt, or to taste
2 cups cubed (1/2-inch) firm-textured white bread
2 tablespoons unsalted butter