In a saucepan or pot over medium-high heat, add the water, butter and salt and bring to a boil.

Once it starts boiling, add the flour by slowly sifting it through a sieve and mix with a wooden spoon until a smooth, creamy dough forms.

Turn the heat to low and continue cooking, stirring quickly and intensely, taking care not to let the dough stick to the pan. Continue until the dough pulls away from the sides of the pan and becomes dense.

Transfer the hot dough to a mixer bowl or food processor fitted with the paddle attachment.

Start the mixer on low speed and gradually add the mustard, Parmesan and eggs, one at a time, until fully incorporated.

Then mix in the parsley and green onion.

Once the mixture has cooled a little, transfer it to a piping bag and let the dough rest at room temperature for about 15 minutes.

Meanwhile, add water to a large pot and bring it to a boil.

When the water is boiling, squeeze out pieces of gnocchi about 3-4 cm each from the piping bag, cutting each one off with a knife.

Pipe a dozen gnocchi, then boil them for about 3 minutes and lift them out with a slotted spoon or sieve. Transfer them to a bowl greased with a little olive oil and repeat with the rest of the dough. It's best to cook them in batches and not overcrowd the pot, so they don't stick together while cooking.

Let them cool, or freeze them until you are ready to finish the dish.

Prepare the sauce.

In a frying pan over medium heat, add the olive oil and garlic and sauté for a minute. Add the kale leaves and leeks and continue cooking.

Add ½ cup of water and cook, stirring, until the leaves soften and the water evaporates, about 7-8 minutes.

Add the butter and stir until it melts. Turn off the heat, add the Parmesan, salt and pepper and mix until you get a creamy sauce.

Add the gnocchi to the sauce, toss to coat and serve.