1. Trim and roughly chop the leeks and garlic. Place in the bowl fitted with the ultrablade knife and mix at speed 12 for 5 seconds. Scrape down the sides of the bowl.
2. Add butter and oil. Launch the P1 simmer program at 270°F for 5 minutes. Scrape down the sides of the bowl.
3. Peel the potatoes and cut into 1-inch pieces. Add potatoes and broth to the bowl and launch the P2 soup program 210°F for 50 minutes.
4. At the end of the program, add cream, salt and pepper. Mix at speed 10 for 20 seconds. Top with chopped chives and serve with crusty bread