300g 70%+ cocoa (bittersweet) chocolate, roughly chopped
220g unsalted butter, cut into pieces
6g (1 teaspoon) salt
8.4g (2 teaspoons) vanilla extract
160g (3 whole) eggs, at room temperature
40g cocoa powder
100g broken bourbon biscuit pieces (or choose your favourite biscuit)
220g (‘mature’) 100%-hydration sourdough starter
Preheat the oven to 160C.
Melt together the chocolate and butter in a pan above simmering water. Check it frequently to make sure it doesn’t burn.
Take pan off the heat and whisk in the sugar, salt, and vanilla.
Add the eggs one at a time, whisking to combine after each addition.
Add cocoa powder and broken biscuit pieces over the chocolate mixture and stir to combine.
Add the sourdough starter and stir gently until completely incorporated.
Line a 20 x 30cm metal baking pan with baking paper.
Pour in the mixture and bake for about 40 minutes, until a bamboo skewer inserted in the center comes out clean.
Cool in the pan for 20 minutes, then loosen the edges with a knife, invert onto baking paper, and re-invert onto a wire rack.
When completely cool, cut into squares.