Chocolate Caramel Slice (Millionaire's Shortbread)

INGREDIENTS

1 stick

plus 1 tablespoon (125 g) unsalted butter

1 cup

plain flour, sifted

1 tsp

baking powder

1 cup

dessicated coconut

1/2 cup

caster sugar

1 stick

unsalted butter

14 fluid_ounces

tinned sweetened condensed milk

2 tbsp

golden syrup

1 tsp

vanilla bean extract or vanilla extract

2/3

cup (100 g) light muscovado sugar or light brown sugar, tightly packed (lumps removed)

5 1/2 oz

dark chocolate, 70% cocoa

1 tbsp

vegetable oil

sea salt flakes (such as Maldon Sea Salt)