Chocolate Pastry
1. Combine flour, icing sugar, cocoa powder and salt in a mixing bowl. Add the diced butter and mix on low speed until the butter is completely broken down to breadcrumb consistency. Add the yolk and water and mix just until the dough comes together. Wrap the dough tightly and chill for at least two hours.
2. Roll your dough to a round approximately 26cm wide and 3mm thick. Gently roll over your rolling pin and unroll to drape over your tart shell. Press the dough in so it makes full contact with your tin. If it breaks, tears or is uneven, don’t worry as you can simply press it all into the tin without any negative effects. Trim any excess dough and reserve it for patching potential cracks. Place in the refrigerator while your oven preheats.
3. Preheat the oven to 150°F/170°F. Bake your tart shell for 5 minutes before checking for slumping. If the pastry is slumping, gently push it up the sides back into shape with a glass or measuring cup. Continue baking for 15 minutes or until fully baked and dry to the touch. Brush with a thin layer of egg wash and place back in the oven for 2 minutes to just to dry. Let cool.
Chocolate Custard
1. Place the chocolate in a bowl over a saucepan with one inch of water and bring to a simmer. Let sit until the chocolate is fully melted, stirring occasionally. Turn off the heat but leave the bowl over the steaming water so it remains fluid.
2. Combine the cream, milk, salt, and golden syrup, and whisk to combine.
3. Add cocoa powder to a saucepan and gradually add the cream mixture, whisking constantly to prevent lumps from forming. Once all the cream is added and you have a smooth mixture, bring it to a simmer over medium heat. Bring the cocoa cream to a simmer, stirring constantly. This will help the cocoa bloom to maximise its flavour, but it can easily burn and turn very bitter, so stay with it. Once your mix is just simmering, stream slowly into a bowl with the egg yolks, stirring constantly.
4. Pour the hot custard over the melted chocolate and let it stand for one minute. After one minute, gently stir in small circles from the inside to emulsify in the melted chocolate while incorporating minimal air bubbles. When the mixture is fully incorporated, smooth and glossy, pour it into your prepared tart shell.
5. Allow to set in the fridge for at least 6 hours before slicing.
