Preheat oven to 375°.
To prepare soup, melt butter in a Dutch oven over medium heat. Add leek; cook 10 minutes or until tender, stirring occasionally (do not brown).
Add potatoes, water, salt, broth, and 2 thyme sprigs. Bring to a boil; reduce heat, and simmer, uncovered, 20 minutes or until potatoes are very tender.
To prepare cheddar toasts, place baguette slices in a single layer on a baking sheet. Bake at 375° for 7 minutes or until toasted. Turn slices over; coat with cooking spray, and sprinkle 1 tablespoon cheese over each slice. Bake 5 minutes or until cheese melts. Sprinkle evenly with red pepper.
Remove pan from heat; discard thyme sprigs. Partially mash potatoes with a potato masher; stir in cream. Sprinkle with black pepper. Serve with cheddar toasts. Garnish with thyme sprigs, if desired.