Bring a large pot of water to the boil and add a good pinch of salt. Add the tagliatelle,potatoes and green beans (all in the same pot) and cook for about 9 minutes,or until the pasta is al dente.
Meanwhile,in a small bowl,combine the basil,olive oil,lemon juice,grated parmesan and a pinch of salt. Mix well.
Drain the pasta,potatoes and beans and return them to the hot pot. Add the basil mixture and toss until well combined.
Serve topped with shaved parmesan and drizzle with extra olive oil (optional).