Heat the butter in a large pot over medium heat; add in the leek, celery, garlic, red pepper flakes, sugar, curry powder and cumin; cook stirring for 3-4 minutes.
Add in the chopped butternut squash, broth (or water) and apples; bring to a boil.
Reduce heat and simmer for 30-40 minutes or until the squash is tender.
Place half of the broth in a blender; process until smooth; transfer to a heat-proof bowl.
Repeat with the remaining soup; return to the pot along with the soup from the bowl.
Add in evaporated milk or whipping cream; cook for 2-3 minutes to heat through.
Season with salt and lots black pepper.
Ladle into bowls and sprinkle with croutons.