Potato leek soup recipe with sourdough baguette

Ingredients

• 1 package dry active yeast (2 1/2 teaspoons)
• 3 1/2 cups unbleached flour (bread flour)
• 2 1/4 teaspoon salt
• 1 1/3 cups cold water plus 1/3 or so additional water
• 2 Tablespoons butter
• 3 cups sliced leeks, white and palest green, trimmed and rinsed.
• 1 1/2 cups sliced onions about 6 ounces or 2 medium.
• 2 tablespoons flour
• 6 cups water
• 4 cups peeled diced potatoes, preferably russets, cut into 2 inch chunks about 1 1 /2 pounds
• 1 1/2 teaspoon of salt or to taste
• 1/2 teaspoon fresh ground white pepper or to taste