Place sweet potatoes into a large pot and cover with water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain and allow sweet potatoes to cool. Peel sweet potatoes, transfer to a bowl, and mash.
Heat a skillet over low heat; cook and stir almonds in the hot skillet until lightly toasted and fragrant, about 1 minute.
Beat 1 egg in a small bowl.
Mix beaten egg, almonds, milk, and honey into mashed sweet potatoes. Divide sweet potato mixture into 15 equal parts. Shape each manju into a sweet potato-shape; arrange on a baking sheet.
Beat remaining 1 egg and water together in a bowl. Brush egg mixture over each manju; top with peanuts.
Bake in the preheated oven until manju are golden brown, about 25 minutes.