Boil enough water to cook the pasta in, salt the water and cook the pasta in it. Drain and keep aside.

Peel and cut the potatoes into rough cubes. Heat the stock in a pan and boil the potatoes in it.

Meanwhile, heat the butter in a large pan, add the leeks, onions and garlic to it. Saute over medium heat till they soften. Be sure to not let them brown. Add salt and some of the black pepper to this and mix well.

Once the potatoes are done (they should be cooked through and almost falling apart), add the potatoes along with the stock to the pan with the onions and leeks in it. Add a little water or a little more stock if it is too thick. Let it all come to a boil. Mash the potatoes with the back of a ladle till it all gets creamy.

Reduce the heat and add the buttermilk and switch off heat immediately. Add the cooked and drained pasta to this and mix well. If you feel the need for more sauce, add more butter milk or cream to it. Top with some fresh cracked pepper and serve immediately.