In a large pot or Dutch oven set over medium heat, melt a few tablespoons of butter then add the chopped onion, carrots and celery. No need to chop the vegetables too fine, you'll be blending the soup later anyway.
Allow to cook until the veg starts to soften and turn a light golden color then stir in the garlic, sage and a pinch of chilli flakes.
Cook for 30 seconds then add the peeled and cubed sweet potato. Pour in the broth/stock and season with salt and pepper, to taste.
Bring the soup to a simmer then cover with a lid, reduce the heat and allow to cook gently for 20-30 minutes until the vegetables are fork-tender.
Pour the cream into the soup then blend with an immersion blender. Alternatively, transfer the soup to a blender and blend until smooth.
Season to taste.
To make the toasts, mix the softened butter with minced garlic, finely chopped sage and grated Parmesan cheese.
Slice the baguette into slices then transfer to a baking sheet.
Spread the garlic sage butter over each slice of bread then transfer to a hot oven and bake for a few minutes until crisp and golden.
Serve the soup with a drizzle of cream and crispy sage leaves (optional) with the toasts.