Pre heat the oven to 190c;
Peel and cut the potatoes into roughly 3 inch blocks, peel and cut the onions into quarters and place on the bottom of a roasting tray place the potatoes on top, the garlic and drizzle the olive oil over the top, place into the oven and cook until the potatoes are cooked through about 40 to 45 minutes.
Pass the potatoes and onion mix through a food mill and place into a mixer. Add the chopped parsley, Parmigiano and nutmeg, truffle and mix to incorporate, season with salt and pepper cover and leave to cool in the fridge.
Place all the ingredients into a mixing bowl with the dough hook attachment and mix on slow speed until smooth dough has formed. Wrap and refrigerate for 2 hours allowing resting before using.
Fold in the pasta machine and continue to roll and fold the pasta through the machine many times to “laminate” the pasta. Roll out the dough to a thin sheet and cut out 8 cm diameter circles.
Place 20gm of the potato mixture into the centre of the circle and fold the circle in half. Join the two corners of the semi-circle, bringing them towards yourself and join the ends by pressing the pasta together between the fingers to stick.
Cut the butter into small pieces and place into a mixer with the paddle attachment and beat on medium speed until creamed. Season with the grated truffle and sea salt flakes and beat until mixed in, remove from the mixer and place into an airtight container until needed.
Bring a large pot of salted water to the boil. Place the tortellini in the water and cook for 2 to 3 minutes.
Heat the butter in pan until the butter starts to colour. Strain the tortellini and toss together adding a little of the pasta water to emulsify the butter.
Spoon the tortellini onto serving plate grate some Parmiggiano over and shave with a generous amount of truffle.