Sourdough Rye Brownies

Place all the stage 1 ingredients in a 300ml (½ pint) jar or container with a lid, mix, cover and leave at warm room temperature for 4–6 hours.
Place the stage 2 ingredients plus 125g (4 oz) of the starter in a large bowl, stir well with a whisk, cover and leave in a warm place for 1–2 hours or more time if it suits you. It won’t rise much but you should see some bubbles as evidence of fermentation on the surface of the mix.
In the hour before you plan to do the final mix and bake, melt the butter and chocolate in a small heatproof bowl over a pan of simmering water. Set aside to cool for 30 minutes. Line a 25cm (10 in) square tin with baking parchment.
Preheat the oven to 160ºC/325ºF/gas mark 3.
Add the melted chocolate and butter plus the remaining stage 3 ingredients into the bowl with the batter. Whisk until well combined. Pour into the lined tin and smooth the top with the back of a spoon so it is evenly distributed.
Bake for 30-40 minutes until the top looks dry but it still has a slight wobble. It’s difficult to overbake these. Sprinkle with additional sea salt, if liked, after they come out of the oven and leave to cool in the tin. When cool cut into squares to serve. The brownies can be stored in an airtight container for up to a week.