Melt butter in a saucepan. Add flour and stir for about one minute. Butter should still remain white in color.
Add milk and cream and whisk vigorously to prevent lumps from forming. Cook, whisking constantly, until it begins to thicken. Let it simmer for a few minutes, whisking from time to time. Season with salt, white pepper and nutmeg.
Add roasted garlic, potatoes and Parmesan. Using immersion blender (or regular blender) blend until smooth.
Serving suggestion: top the soup with some shaved Parmesan cheese, drizzle with some olive oil and sprinkle with red pepper flakes.
*If you don't have roasted garlic at hand, slice fresh garlic and fry it in a little bit of olive oil for a very short time (be careful not to burn it).