Lightly grease a medium loaf pan (8 ½ x 4 ½ x 2 ½) with the oil.

Mix the gelatin, water and extract in a medium pot. Add the icing sugar and whisk vigorously.

Cook the mixture over medium heat, whisking continuously until the sugar and gelatin has completely dissolved.

Then bring the mixture to a boil. Once the mixture is bubbling, reduce the heat and simmer for 20 minutes. Avoid stirring the pot from this point.

After about 20 minutes the mixture should become thick and syrupy. Remove the pot from heat and add a few drops of food colouring, stirring until the colour is even.

Stir in the chopped nuts (and zest, if using), and then leave the mixture to cool for a couple of minutes.

Pour the mixture into the loaf pan, cover with a dishcloth, and leave it to set at room temperature for 24 hours.

Mix the cornstarch and icing sugar together well and sift to remove any lumps. Set this dusting mixture aside for later.

Once the Turkish Delight has set, use a butter knife to score around the edges of the pan. Carefully pull the candy out of the pan with your hands and turn it out onto a flat surface that has been sprinkled with some of the cornstarch and icing sugar mixture.

Use a sharp knife to cut the Turkish Delight into squares, wiping the blade as needed with a damp cloth.

Roll your Turkish Delight blocks in the dusting mixture until well coated, then store in an airtight container.