Add the plain flour, olive oil and salt and pepper to a large mixing bowl. Gradually adding the water, knead the mixture with clean hands until it comes together into a dough. The dough should be moist but not overly sticky, so you may not need all of the water (or you may need a dash more!).
Continue to knead for a few more minutes, until the dough is fairly elastic. Place the ball of dough into a lightly oiled bowl, and cover with a tea towel. Leave to rest for 1 hour.
While the dough is resting, prepare the filling. Remove any tough stems from the kale, and chop the leaves. Add the finely diced onion, garlic and parsley, along with a tbsp of olive oil and a touch more salt and pepper. Mix well, and set aside.
When the dough has rested, transfer it to a lightly floured surface. Divide the mixture in two, and roll the first section out to your desired size (the thinner the better). My baking tray measured around 12 x 9 inches, so I kept this in mind when rolling.
Transfer the rolled-out dough to a sheet of baking paper, and add the kale filling, making sure it's spread out evenly to the edges of the dough.
Roll out the second piece of dough in the same way, and place it over the kale filling.
Using a rolling pin, press the two layers of dough together over the filling, pressing out as much air as possible and tightly sealing the edges. Make a few small holes in the top of the pie with a fork.
Bake at 190°C (Gas Mark 5 / 375°F) for around 20 minutes, until lightly browned. Cut into diamonds with a pizza cutter, and serve warm, drizzled with extra virgin olive oil if desired.