For the tortellini, place the flour and two of the eggs into a food processor and pulse until the mixture resembles breadcrumbs. Turn the mixture out onto a floured work surface and gently work the mixture together to form a dough.
Lightly knead the dough for 2-3 minutes, or until it is smooth and elastic. Roll into a ball, cover with cling film and chill in the fridge for at least 20 minutes.
Meanwhile, cook the kale in a pan of boiling water for 2-3 minutes, or until wilted and just tender. Drain well, wrap in kitchen paper and squeeze out any excess moisture from the kale.
Finely chop the kale, then place into a bowl along with the ricotta. Season with salt and freshly ground black pepper, some freshly grated nutmeg and the lemon zest. Mix until well combined. Set aside until needed.
Remove the dough from the fridge and discard the cling film. Lightly flour your pasta machine to prevent the dough from sticking. Flatten the dough ball slightly with a rolling pin, then starting at the lowest (thickest) setting, feed the dough through the machine, turning the handle with one hand and holding the dough as it comes through the machine with the other.
Change the setting on the pasta machine to the next-thickest setting, flour it again and feed the pasta sheet through the machine again, as before. Repeat this process, flouring the machine and changing the setting down each time, until you reach the thinnest setting. You can cut the pasta into smaller individual sheets and work on them individually, keeping the remaining unused dough covered under cling film to prevent them from drying out.
Beat the remaining egg in a bowl. Cut out circles from the pasta sheets using a 4-5cm/1.5-2in pastry cutter, then brush each circle with the beaten egg. Place a heaped teaspoon of the kale and ricotta filling onto one half of the circle, then fold the other half of the pasta over, so that it forms a half-moon shape, and press together to seal. Bring the bottom two corners of the half-moon together to create a circle and pinch to seal. Repeat with the remaining pasta and filling mixture, placing each completed tortellini on a tray lined with greaseproof paper. Set aside.
For the turbot, season the fish with salt and freshly ground black pepper. Heat a frying pan until hot and add 25g/1oz of the butter. When the butter is foaming, add the turbot and fry skin-side down for 2-3 minutes, or until the skin is crisp and golden-brown.
Flip the fish over and cook for further 2-3 minutes, or until cooked through (the flesh should be opaque and flake easily). Remove the fish from the pan and set aside to rest.
Return the pan to the heat and add 50g/2oz of the butter to the pan. Cook over a medium heat for 4-5 minutes, or until the butter turns a light nut-brown colour. Stir in the capers and lemon juice, then remove the pan from the heat and stir in the chopped chives and parsley. Season, to taste, with salt and freshly ground black pepper.
Heat a large lidded pan until hot, add the remaining butter and fry the kale for about 1-2 minutes. Add the water, cover the pan with the lid and cook for 2-3 minutes, or until most of the water is absorbed and the kale is just tender. Remove from the heat and keep warm.
Cook the tortellini, in batches, in a pan of boiling salted water for 2-3 minutes, or until they float to the surface and are al dente. Remove with a slotted spoon.
To serve, spoon the wilted kale into the centre of four serving plates. Place a turbot fillet, skin side up, on top of the kale and arrange 4-5 tortellini on the fillet. Drizzle the caper butter over the top and serve.