Boil the potatoes with their skins on in well salted water - I used about 1 tsp salt in the water. Cook until you can just run a fork or knife through the potatoes then drain the water off. If you boil them for too long then excess water will seep into the potatoes.
Skin the potatoes while they're still hot and pass them through the Mouli (food mill, potato ricer, sieve) until no lumps can be seen. I skinned the potatoes by scraping the skin away with a butter knife and made sure not to squish the potato ribbons coming out of my own sieve since you're trying to get as much air as possible into the mash.
Beat the eggs and then pour them into a well you've made in the centre of your mash. Stir it in well and then gradually add the sifted flour, salt, and Porcini powder, mixing well. The end result should remind you of pastry dough.
Flour your work surface and roll the gnocchi dough out to a thickness of about 1/2cm (1/4") and then slice the dough into 2.5 cm/ 1" thick ribbons.
Roll each ribbon into a 'sausage' and then line them up side by side. Cut across the entire line of rolls so that you have pieces about 2.5cm / 1" long. Press the back of a fork into the top of each and then form each Gnocchi into a regular shape. The gnocchi will initially be a golden doughy colour but will darken if you keep them overnight in the refrigerator.
Bring a pan of water to a boil and add your gnocchi one at a time and allow to boil until the little dumplings are all floating at the surface of the water. It will take about ten or fifteen minutes and if you allow them to boil while you're making the sauce then both sauce and gnocchi should be ready at the same time.
Make the Sauce
Reconstitute the dried porcini by adding them to the 100ml boiling water. They'll need about ten minutes to soften up.
Melt the butter in a pan and then add the garlic. I passed my cloves through a garlic press but you can also mince them finely. Cook until soft and fragrant then add the salt, cream and porcini mushrooms, water and all.
Add the sliced mushrooms and allow to cook on medium-low until the mushrooms are soft.
Add the drained gnocchi to the sauce along with the Parmesan cheese. Stir well and then add the chives and baby spinach. Serve immediately and enjoy ~