In a large saucepan over medium-high heat, melt the butter. Add the leeks and cook, stirring, for 5 to 6 minutes, until wilted.
Add the stock, potatoes, and carrots. Bring to a boil and cook for 10 to 15 minutes, until softened and fork-tender, depending on the size of the vegetables.
Add the salmon and cream and bring to a simmer. Cook for 5 to 6 minutes, until the salmon is cooked through; season with salt and pepper.
Divide the soup among bowls. Top with the dill.