Recipe by Halen Mon found in their new book 'Sea Salt', available to order here.
This tart is incredibly easy to make, but tastes and looks as impressive as the finest French patisserie. The contrast between the thin crisp base and the rich chocolate ganache is what makes it a winner.
100g/3.oz butter, at room temperature, plus extra for greasing
Preheat the oven to 180C/160C fan/350F/Gas 4. Lightly grease the base and sides of a 23cm/9in loose-bottomed tart tin with butter and line the base of the tin with baking paper. Pulse the biscuits, cocoa powder and a pinch of fine salt together in a food processor until a fine crumb forms, then transfer to a large bowl. Melt 50g/1.oz of the butter in a small saucepan, then pour it over the biscuit mixture and stir until the mixture is combined and resembles wet sand. Using a clean, flat-bottomed glass, pack the biscuit mixture evenly into the prepared tin, shaping it around the sides so that it meets the rim at the top all around the edge. Bake the biscuit case in the oven for 10–12 minutes until it starts to look darker around the top. Leave to cool completely.
Meanwhile, pour the cream into a medium saucepan, leaving at least 5cm/2in of space between the surface of the cream and the top of the pan and heat until you see bubbles start to form around the side of the pan. Remove from the heat and scatter both chocolates over the cream so that it covers as much of the surface of the cream as possible, rather than forming a pile in the centre. Leave for 1 minute without stirring, then stir to combine. The mixture should be thick and glossy. Cut the remaining 50g/1.oz butter into six pieces and whisk into the chocolate mixture, a piece at a time, until smooth. Stir in the vanilla and rum, then pour the chocolate mixture into the prepared tin, without letting any spill over the sides of the biscuit case. Shake the tin gently to distribute the chocolate filling evenly, then chill in the fridge for 90 minutes. Remove the tart from the fridge and scatter over a generous pinch of flaked salt (any earlier and the salt will sink into the chocolate mixture). Chill for at least another hour, or up to 24 hours before slicing. Serve with créme fraîche and fresh berries. The tart will keep covered in the fridge for up to three days.