Heat the oven to 180C (160C fan)/350F/gas mark 4 and, if using kataifi, melt the butter or oil on a shallow rimmed baking tray.

Roughly chop the kataifi, toss it in the melted butter, then bake, stirring every 10 minutes so it colours evenly, for about 30 minutes, until golden. Remove and leave to cool.

If using cornflakes, simply roughly crush them into shards.

Tip the raw pistachios on to another baking tray large enough to hold them all in a single layer, and bake alongside the kataifi for about 15 minutes, until they smell toasty. Remove, leave to cool, then, to remove some of the skins, either rub them in a clean tea towel or shake vigorously in a large jar to help dislodge the papery husks, then remove by hand.

Roughly chop the nuts.

If using white chocolate, melt it in a heatproof bowl set over but not touching a pan of simmering water, then stir in a couple of drops of green food colouring, if using.

Spoon or drizzle the white chocolate mix over the base of the chocolate bar mould, then put it in the fridge to set while you melt the remaining chocolate.

Chop the milk or dark chocolate. If you're tempering it, melt 110 g of the chocolate as above, to 40-45C for milk and 46-48C for dark, then stir in the remaining 50 g until melted. Cool to 26C for milk and 27C for dark, then heat back to 29C (milk) or 31C (dark) before use.

Tip just enough of the melted chocolate into the mould thoroughly to coat the white chocolate base, then chill for about 30 minutes until set firm.

Meanwhile, whizz the chopped pistachios in a food processor or blender until they're fairly finely ground and beginning to look slightly oily and to clump together, then add the coconut oil or tahini and whizz again to combine.

Add the milk powder, icing sugar and a pinch of salt and whizz again. Taste and add more sugar if you'd like it sweeter. If using salted pistachios, roughly chop them, then stir in.

Once you're ready to fill, stir the kataifi into the pistachio mixture until well combined, then spoon into the chocolate shell and level the top, leaving a small gap around the edge.

Re-warm the remaining melted chocolate, then pour it all over the top. Chill for at least two hours, or until completely set, before turning out.

For individual truffles, make the filling as above, then spoon small, roughly 20 g balls of it on to a tray and chill for about 30 minutes, until firm, while you're melting the milk or dark chocolate.

Dip the balls in chocolate to coat, then return to the fridge to set. Decorate with the green white chocolate once firm, or put a whole pistachio on top while the balls are still slightly tacky.