Bring a large pot of water to a boil. Season with salt and add macaroni. Cook as directed on the box for approximately 7 minutes. Drain and set aside
Meanwhile heat a shallow saucepan over high heat. Add the clams and shake the pan so the clams are in an even layer. Add the sake and cover the pan and cook until the clams open and release their juices, 3-5 minutes depending on the size of the clams.
Add the pesto and the cooked pasta to the clams and toss gently until everything is coasted with the pesto. Taste and adjust seasoning with salt and pepper. Garnish with shiso and serve immediately.
Note: the nori pesto can be made the day before and stored in the fridge. Bring to room temperature before using.