24 brownies (9 x 13-inch pan)
Mix: 10 minutes
Bake: 40 minutes
300 g 72% cocoa solids chocolate, chopped into chunks
226 g unsalted butter, cut into pieces
200 g dark brown sugar
6 g salt
8 g vanilla extract
3 whole medium eggs, at room temperature
40 g cocoa powder
220 g mature 100%-hydration sourdough starter
Preheat the oven to 325F.
Butter a 9 x 13-inch metal baking pan. Line the bottom of the pan with parchment, and butter the parchment.
In the microwave, melt together the chocolate and the butter. Max power for 25 seconds at a time, stirring between each 25 seconds. It should take 3 sets of 25 secs to melt.
Whisk in the sugar, salt, and vanilla.
Add the eggs one at a time, whisking to combine after each addition.
Sift the cocoa powder over the chocolate mixture and stir to combine.
Add the starter and stir gently until it is completely incorporated.
Turn the batter into the prepared pan and bake for about 40 minutes, until a bamboo skewer inserted in the centre come out clean.
Cool in the pan for 20 minutes, then loosen the edges with a knife, invert onto parchment paper, and re-invert onto a cooling rack.
When completely cool, cut into squares.
And here are a few more pictures.