Pre-heat your oven to 180c, fan forced. Place the potatoes on a baking tray and pop in the oven for 40 - 45 minutes, or until the potatoes are cooked through. Insert a knife or skewer through the centre to make sure they are cooked through.
Remove the potatoes from the oven and slice them open down the centre allowing the steam to escape. When cool enough to handle, remove the potato flesh from the skins (you can roast the skins up again to crispy chips!).
Place the potato in a sieve with large holes and use the back of a spoon to push the potato through the sieve into a large mixing bowl on the underside of the sieve. You will need to use a fair bit of elbow grease! Scrape the potato from the underside of the sieve as you go into the bowl. (If you own a mouli then obviously use this - I don't have one, hence the sieve version. Otherwise you can just mash the potato with a regular potato masher, but make sure you get it really smooth).
One all the potato is in the mixing bowl sift in the potato starch flour and the sorghum flour, then season the mix with salt and pepper. Use your hands to knead the mixture bringing everything together. You can either do this in the bowl or turn everything out onto a floured bench. Knead the mixture for a good few minutes until it comes together into a lovely formed dough. Place back in the bowl and cover with a wet towel and leave to rest for 30 minutes.
Dust your bench top liberally with flour and then take the rested dough and place on the bench. Cut the dough into four pieces and then take one of the pieces and use your hands to roll it out into a sausage shape, around the diameter of a 10c piece. Use a sharp knife to cut the sausage shaped dough into gnocchi pieces, about 2cm lengths. Repeat with the remaining dough. Place the gnocchi onto a floured plate and cover if not using straight away.
Bring a large fry pan to a medium - high heat and add in 2 tablespoons of extra virgin olive oil. Add the sliced mushrooms and season them well with salt and pepper. Toss them through the oil and allow them to really golden up. You want to cook them past being just softened. The idea is to get them nice and crispy on the edges.
In the mean time bring a large saucepan of salted water to the boil. Once the water is boiling add in half of the gnocchi. Once the gnocchi rises to the top of the water use a slotted spoon to carefully remove them and set aside to drain. Repeat with remaining gnocchi.
Now add the sage leaves and garlic in with the mushrooms and an extra 2 tablespoons of extra virgin olive oil. Toss through allowing the sage to crisp up, its should only take a few minutes. Add the pine nuts and toss again.
Add the drained gnocchi to the fry pan with the remaining 1/4-cup of extra virgin olive oil and toss very gently to ensure the gnocchi is covered in all the juices. Season well and then serve immediately.