Preheat oven to 400°F. Peel and dice potatoes and carrots and cut leeks into rounds. Try to cut them roughly the same size so they can cook evenly.
Place the vegetables on a baking sheet lined with parchment paper. Drizzle with olive oil. Trim the top off the garlic cloves, drizzle with olive oil and wrap in aluminum foil.
Mix the spices (turmeric, ginger, garlic powder, onion powder, smoked paprika, salt and freshly ground pepper) in a small bowl. Sprinkle over the vegetables and rub it all over them.
Roast until golden-brown and the vegetables can be easily pierced with a fork, about 30-35 minutes. Stir them 1-2 times during roasting.
Let the vegetables cool a little bit then transfer them in a large pot (if using an immersion blender) or in a normal blender. Squeeze garlic cloves out of their papers. Add 2 cups chicken or vegetable stock and blend until smooth and creamy.
Then add ½ cup stock at a time to thin it to your desired consistency.
Taste for seasoning, pour it in a large pot and warm it up. Serve with fresh herbs, heavy cream and buttered bread slices.