1. Preheat the oven to 180°C, gas mark 4. Grease and line a 20cm square cake tin with baking parchment. Melt the butter and chocolate in a heatproof bowl set over a pan of gently simmering water, then remove from the heat and beat in the sugar.
2. Beat in the eggs, one at a time, until smooth then beat in the stem ginger syrup. Sift in the flour and ginger into a bowl then fold into the chocolate mixture. Fold in the chocolate chunks and chopped stem ginger.
3. Heat the caramel sauce according to the instructions on the jar then pour into a small bowl and stir in the sea salt.
4. Pour half of the chocolate mixture into the prepared tin and smooth out with the back of a spoon. Spoon the caramel sauce over the top then use a small skewer to swirl into the chocolate mixture. Pour the rest of the chocolate mixture over the top, ensuring all of the caramel is covered.
5. Give the tin a couple of sharp taps on the work surface to knock out any air bubbles, then bake for 1 hour.
6. Just before the brownies have finished baking, half fill a large roasting tin or the sink with cold water and add a handful of ice cubes. Once the brownies have finished baking, set the tin in the ice bath for 30 minutes to stop them from continuing to cook in the tin.
7. Once completely cool turn out and cut into 16 squares.
Courtesy of Waitrose