Preheat oven to 200 C (400 F) Pierce each potato 3 - 4 times with a sharp knife. Spread rock salt out on a small oven tray, place potatoes on top and roast for 1 hour, or until soft.
Meanwhile, sift flours into a bowl and whisk to throroughly combine. Set aside. Trim beetroot stems to 2 - 3cm long. Place in a small saucepan, cover with plenty of water, and bring to the boil. Turn heat down and simmer for 45 - 60 minutes or until tender. Drain and set aside to cool for 5 minutes. Peel and roughly chop, then place in a small food processor and puree, stopping to scrape down the sides a few times to ensure even blending.
Remove potatoes from oven and set aside to cool for 5 minutes, just enough to handle. Peel, and either push through a potato ricer or mash well. Stir beetroot puree through mashed potato aong with egg yolk and salt. Add flours and mix to form a soft dough. The dough will still seem a little tacky, but shouldn't stick to your hands. Turn out onto a clean lightly floured bench and knead a few times until dough comes together in a ball. Cover with a tea towel and leave for 10 minutes.
To make gremolata, heat the olive oil in a fry pan over medium heat. Add the leek and fry, stirring frequently, until it softens and just starts to brown. Add the capers, lemon rind and juice and stir a minute or so to combine. Remove from heat.
Bring a large saucepan of water to the boil. Cut dough into four pieces, rolling each into long ropes approx. 2cm wide. Use a floured knife to cut off 3 cm pieces. Roll over the prongs of a fork to create slight edges in each gnocchi dumpling.
Add the gnocchi to the boiling water and cook a minute or 2, or until they float to the surface. Note that you will most likely need to do this in batches, depending on the size of your pot.
Use a slotted spoon to remove the cooked gnocchi, and add to the pan with the gremolata. Stir to combine, and serve immediately.
Recipe by to her core at http://tohercore.com/beetroot-gnocchi-w-caper-leek-gremolata/