Line a 26 x 16 cm tin with baking parchment. Break up the chocolate and place in pan with condensed milk. Gently heat until the chocolate melts and remove from the heat. Stir to combine and then add the cherry ripe and pistachios and stir again.
Spoon into the lined tray and smooth the top. Place in the fridge and when the fudge is set, cut into squares.