Method

• 1.
  Sift the cocoa and flour into a large mixing bowl. Add a pinch of salt flakes and 125g of the cold butter. Using your fingers, work the butter into the flour until mixture resembles breadcrumbs. Work in the egg and 1 tbs cold water, and bring together to form a dough. If it looks too dry, add a few teaspoons of cold water. Place in an oiled mixing bowl, cover and chill for 30 minutes.
• 2.
  Butter a 23cm x 2.5cm-deep, loose-base tart pan. Tip dough out onto a lightly floured clean work surface and roll into a circle large enough to cover the pan base and sides with a slight overhang. Keep turning the dough so it does not stick. Using your rolling pin, lift the dough over the tart pan, gently press it down into the base and push the pastry into the sides. Trim off any excess. Scrunch up some baking paper, unfold it, place it into the pastry-lined pan and fill with baking beans. Rest in the refrigerator for 15 minutes.
• 3.
  Preheat oven to 200°C. Bake pastry for 15 minutes, then remove the beans and paper, and bake for a further 5 minutes to cook the base or until light golden and dry to touch. Remove from oven. If the base has puffed up, gently put the beans in the baking paper and back into the case and the base will deflate. Stand on a wire rack and cool completely in the pan.
• 4.
  Meanwhile, place the remaining 50g butter into a small saucepan and pour in the cream and sugar. Heat over a low heat, stirring occasionally, for 5-6 minutes or until the cream has warmed but not bubbling. Remove from the heat and stir in the chocolate until combined and smooth.

• 5.
  Break up 120g of the halva into small pieces and arrange over the bottom of the pastry case (it’s nice to have a few bigger chunks for texture). Pour over the chocolate mixture and smooth out with a small palette knife. Refrigerate for 2-3 hours or until set. Sprinkle with sea salt and scatter with the remaining halva. Slice to serve.