In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for about 5 minutes until translucent. Add the minced garlic and cook for an additional minute until fragrant.
Stir in the diced carrots and potatoes, and cook for another 5 minutes, stirring occasionally.
Pour in the vegetable broth and water. Add the salt and black pepper. Bring the mixture to a boil, then reduce the heat and let it simmer for about 15 minutes, or until the vegetables are tender.
Add the pierogi to the pot and cook for an additional 5-7 minutes, or until they are heated through.
Stir in the heavy cream and fresh dill, and let the soup simmer for another 2-3 minutes. Adjust seasoning if necessary.
Serve hot, garnished with chopped chives if desired.