Method

• 1.
  For the filling, heat the butter in a heavy-based pan over a medium-high heat. When it’s foaming, add the sliced onion, celeriac and garlic, season and cook, stirring regularly, for 10-15 minutes until the vegetables soften and caramelise lightly.
• 2.
  Add the chopped sage to the pan and stir well. Cook for a further few minutes, then pour in the stock. Put a lid on the pan, bring up to a simmer, then turn down the heat and cook gently for 15-20 minutes until the celeriac is very tender.
• 3.
  Use a slotted spoon to lift the veg from the pan into the jug of a blender or food processor. Whiz until you have a thick, smooth puree. Gradually add more liquid, if needed, to achieve the right texture. Taste and season, then spoon into a bowl, cover and chill.
• 4.
  For the pasta, place the flour in a large bowl with the salt. Make a well in the centre and crack in the eggs. Use a fork to whisk the eggs together, then slowly incorporate the flour a little at a time. Once you have a soft dough, tip it out onto a clean work surface and knead for 8-10 minutes until it’s smooth and silky. Wrap the dough, then rest in the fridge for 30-40 minutes.
• 5.
  Divide the rested dough in half and work each piece into a flat rectangle. Pass one rectangle through the pasta machine on its thickest setting a few times. Then fold the dough into thirds and pass it through twice more on the thickest setting (this helps to give it structure).
• 6.
  Run the dough through all the machine’s settings, from its thickest to its second- thinnest, dusting both sides of the pasta lightly with flour each time you roll. After the second-thinnest setting, cut the pasta in half widthways and lay the two sheets on a floured surface. (If you don’t have a pasta machine, roll out the dough with a large rolling pin – get it as thin as you can.) Repeat with the second rectangle.
• 7.
  Place heaped teaspoonfuls of the celeriac mixture 4-5cm apart along half of one sheet of pasta, using no more than about a quarter of the mixture. You should be able to fit 14-16 teaspoons along its length.
• 8.
  Use a wet pastry brush to dampen the pasta around the filling. Carefully fold the other half of the pasta over, gently pressing it down around the filling, easing out any air pockets as you go. Using a sharp knife, trim the pasta into even squares, then lay them out on a tray well-dusted with flour. Dot the filling over the other pasta sheet and enclose in the same way. Sprinkle the ravioli with a little semolina and avoid stacking them on top of each other as they may stick. Repeat with the other two pasta sheets.
• 9.
  To cook the pasta, bring a large pan of salted water to the boil. Set a large frypan over a low heat. Add the butter to the frypan with the remaining whole sage leaves.
• 10.
  Drop the ravioli in batches into the boiling water. Cook for 3 minutes, then lift out with a slotted spoon and put straight into the pan of bubbling butter, carefully turning to coat.
• 11.
  Add the kale to the simmering pasta water, cook for 1-2 minutes until tender, then drain and stir into the pasta, spooning over the buttery sauce as you go. Divide the ravioli and kale among 4 warmed plates, then crumble over the blue cheese to serve.