Preheat oven to 400 degrees.
Peel and boil the sweet potatoes until soft. In a mixer with a paddle attachment, combine all the ingredients except for the walnuts and the second syrup to form a compound butter.
In a mixer with a whip attachment, add the butter and sweet potatoes. Mix to resemble mashed potatoes. Place sweet potato mixture into an oven-safe pan and cover the top with toasted walnuts, drizzle with second syrup.
Place in the oven for 4-5 minutes. Serve warm.