1 To make the broth, place the carcasses in a pot large enough for the bones. Cover with about 2.5 litres of cold water (too much water will dilute the flavour) and bring just to the boil. Reduce the heat immediately to barely a simmer and, using a large spoon or ladle, skim off the fat and any scum from the surface. Add the rest of the ingredients, all of which should lie on top of the carcasses. Skim once more.
2 The very gently simmering stock will now rise and fall through the vegetables, which act as a filter, absorbing all of the gunk from the liquid and leaving it crystal clear. Leave it to simmer like this for 2-3 hours, tasting regularly. You should eventually notice the point at which the flavour stops improving. This means it’s ready.
3 Remove the pan from the heat and strain the stock in a colander set over a bowl. Then pass the stock through a fine sieve into a 2.5 litre jug. Cover and allow to cool, and place in the fridge overnight. Skim off any fat that settles on top and spoon out the now-jellied stock into a tub – you can freeze if making ahead of time.
4 To make the pasta, place the flour in a food processor and start blitzing. Add the whole egg and the yolks and keep whizzing. You’re looking for a mixture that resembles fine breadcrumbs or couscous – not dusty, nor a big, gooey ball. Add more flour or a few drops of egg until it’s spot on, and don’t rush. The more you run the machine the more you will activate the gluten in the flour, and the better the dough will be.
5 Tip out the dough onto a clean work surface and form into a ball. Knead briskly for 1 minute. Wrap in clingfilm and rest for 1 hour before using (or up to 3-4 hours).
6 Preheat the oven to 180°C, gas mark 4. Place the Portobello mushrooms on a large square of tin foil with a little olive oil and the sliced rehydrated porcini and sliced garlic scattered over. Place the thyme on top, season, then fairly tightly seal into a tin-foil parcel. Cook on a tray in a preheated oven for 30 minutes. Remove from the oven, pour any juices back over the mushrooms. Allow to cool then thinly slice the mushrooms. Discard the thyme but keep the garlic and porcini.
7 Meanwhile, make the tortellini filling. Blend the finely diced chicken, double cream and egg white to a mousse and season. Mix the about ²/3 of the haggis (about 70g) and ¹/3 of the chicken mousse (about 30g) together.
8 Thinly roll out the rested pasta dough and use round cutters to cut 12 x 10cm diameter circles. Place a teaspoon of filling mix on one side of each piece of pasta. Lightly moisten the edge of the pasta with water and fold over the circle, working the edges together with thumb and finger to expel any air. Now dampen the 2 corners of the semi-circle and gently wrap the filled pasta parcel around your little finger to create tortellini shapes. Press gently to seal the two corners together to ensure no filling escapes during cooking. Store on a tray lined with a clean tea cloth.
9 For the pasta, place a pan of salted water on the hob to boil. To another pan, add the salad onions, chopped dried wild mushrooms and sliced truffles with the broth to infuse, and warm through gently. Add the tortellini to the boiling salted water for 4-5 minutes – the filling needs to cook thoroughly. When ready, drain carefully.
10 Place 3 tortellini into a warm shallow bowl. Add the finely sliced cooked Portobello mushrooms, garlic and sliced porcini. Pour a quarter of the broth carefully around the bowl and over the pasta. Season and serve sprinkled with the chopped chives.