Bring the cream and espresso to the boil, remove the pan from the heat. Finely chop the chocolate, add to the pan and stir to melt. Cover the mixture and leave to stand at room temperature for approx. 5 hrs.
To prepare the tin
Grease the sides of a springform pan (approx. 24 cm in diameter).
Mix the flour, cocoa powder, sugar and salt in a bowl. Add the butter in pieces and rub together using your hands to form an even, crumbly mixture. Beat the egg, add and mix quickly to create a soft pastry dough; do not knead. Flatten the pastry, cover and refrigerate for approx. 30 mins.
Roll out 2/3 of the pastry on to the prepared cake tin base, lined with baking paper, close the tin frame. Shape the rest of the dough into a roll and place around the edge of the tin.
Pull upwards approx. 2.5 cm using a spoon handle. Prick the base firmly with a fork. Cover the pastry with baking paper, weigh down with dried pulses.
To blind bake
Approx. 20 mins. in the lower half of an oven preheated to 180°C. Take out of the oven, remove the pulses and baking paper, bake for a further 15 mins. Remove from the oven, remove the tin frame, cool the tart case on a cooling rack.
Add the butter to the chocolate mixture, mix in using the whisk on a hand mixer for approx. 1 min. until the mixture is fluffy and firm. Spoon the mixture into a piping bag with a smooth nozzle (approx. 15 mm in diameter).
Spread the jam over the pastry base. Pipe the chocolate mixture into the tart case in a spiral pattern, dust with cocoa powder. Leave the tart to set in the fridge for approx. 30 mins.