First, prepare the croutons.
In a large bowl, combine the bread cubes with 2 teaspoons (10 ml / 0.3 fl oz) of pumpkin pie spice and toss to coat evenly.
In a large skillet, melt 2 tablespoons (30 ml / 1 fl oz) of butter over medium heat.
Add the seasoned bread cubes and cook for about 8 minutes, turning occasionally, until they are golden brown and toasted.
Set aside.
In a large saucepan or Dutch oven, melt the remaining 2 tablespoons (30 ml / 1 fl oz) of butter over medium heat.
Add the sliced carrots and cook for 2 minutes to soften slightly.
Add the chopped onion, celery, and minced garlic.
Cook for an additional 8 to 10 minutes, stirring occasionally, until all the vegetables are tender and fragrant.
Pour in the vegetable broth, then stir in the pumpkin puree, half-and-half, water, maple syrup, and the remaining 1 teaspoon (5 ml / 0.2 fl oz) of pumpkin pie spice.
Stir until everything is well combined and bring the soup to a gentle simmer to heat through.
Season the soup to your taste with salt and freshly ground black pepper. To serve, ladle the hot soup into bowls and generously top with the homemade spiced croutons and a few fresh celery leaves, if desired.