Add a lug of olive oil to a heavy bottom soup pot and brown the Italian sausage for a few minutes on medium low flame. Use a slotted spoon to transfer it to a bowl and keep warm.
Add the onion with a pinch of sea salt to the pot with the sausage drippings and saute for about 10 minutes until translucent. Stir in the garlic, red pepper flakes and give it a good stir.
Add the 2 tablespoons of butter and allow it to melt. Add the flour and whisk well until incorporated with the oils.
Whisk in the vegetable stock and bring to a gentle simmer.
Add the gnocchi or potatoes and cook together until the gnocchi float to the top, about 3 minutes (or the potatoes have softened)
Add the sausage back into the soup together with the kale or spinach and stir to combine.
In a small bowl whisk together the heavy cream and the egg yolks then gently pour the mixture in the zuppa toscana. Simmer gently for 3 minutes until heated through.
Taste and adjust seasonings with more sea salt.
Serve hot with a drizzle of extra virgin olive oil on top, extra red pepper flakes and crusty bread on the side.