Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with greaseproof paper and pour the rock salt along the middle.
Using a sharp knife, prick the Maris Piper Potato (4) all over and rub with a little Olive Oil (to taste). Place on top of the Rock Salt (250 milliliter) and bake for just oven an hour or until tender. Leave to cool while you make the sauce.
Roast the Beef Marrow Bones (8) in the oven just after you’ve removed the baked potatoes. To do this, arrange the bones on a lined baking sheet and season with Coarse Sea Salt and Pepper (to taste). Roast the bones for about 10 minutes or until browned. Allow to cool slightly.
In the meantime, add Portobello Mushroom (1) to a frying pan and sauté in the Salted Butter (2 tablespoon). Add Fresh Thyme (to taste), along with the Garlic (4 clove). Sauté over low heat until soft and fragrant.
Using a spoon or fork, extract the marrow from within the bones and add to the mushroom sauce and season to taste. Remove the sauce from the heat but keep it warm until needed.
To make the gnocchi, split open the baked potatoes, spoon the insides into a potato ricer and rice into a large mixing bowl. Add the Fine Salt (5 milliliter), yolks of the Egg (2), and All-Purpose Flour (125 milliliter). Use a wooden spoon to combine. Turn the dough out on to a floured surface and gently knead until smooth.
Divide the dough into 4 portions, rolling each into a log about 30 cm (a ruler) in length.
Using a lightly floured knife, cut the logs into 2cm pieces. Here you can either opt for classic gnocchi and roll each dumpling over a floured fork to achieve the identifiable indentations or you could leave the gnocchi as it and sauce them in a little butter instead of boiling.
Arrange the cut gnocchi on a floured tray and cover with a tea towel until ready to cook.
Add a little Extra-Virgin Olive Oil (to taste) to another frying pan and gently sauté each gnocchi dumpling until golden brown on either side. Serve the gnocchi in warmed bowls over a small helping of the Portobello & Bone Marrow sauce and a grating of fresh Parmesan Cheese (to taste).