Heat oil in large nonstick saucepan over low heat. Add onion and garlic, and cook, stirring frequently, until onion is tender, about 5 minutes.
Add sweet potato and 1½ cups (375 mL) of the water to pan. Bring to a boil. Reduce to a simmer, cover, and cook until sweet potato is tender, about 10 minutes.
Stir in pumpkin purée, brown sugar, salt, ground pepper, sage, and remaining 1 cup (250 mL) water, and bring to a boil.
Reduce to a simmer, cover, and cook until flavours have blended, about 5 minutes. Working in batches if necessary, transfer to food processor and purée until smooth.
Return to saucepan and stir in 3/4 cup (175 mL) half-and-half. Cook until heated through, about 2 minutes.
Spoon into soup bowls. With a spoon, drizzle remaining half-and-half over soup. Use the tip of a knife to create a pattern.
Sprinkle Parmesan and cracked pepper on top. Serve with Italian breadsticks and follow with roast poultry and steamed spinach.