Combine all the pastry ingredients together in a food processor. Alternatively, rub the butter into the flour using your fingertips. Add the egg and sugar, knead the mixture to bring it all together. Cover the dough with plastic wrap and refrigerate for at least 30 minutes.
After 30 minutes, remove the pastry dough from the fridge and knead until it is just soft enough to roll out. Place the dough onto a sheet of baking paper. Roll the dough into a rough circle, about 4mm thick. Place the pastry and baking paper onto a baking tray.
Prepare the barbecue for indirect cooking over medium-low heat (as close to 180°C as possible). If using a Weber Q barbecue, set up your barbecue with a convection tray and a trivet.
Sprinkle the cinnamon over the pastry. Lay the fruit on the pastry, leaving an approximate 3cm border around the outside. Drizzle the Chambord over the fruit. Fold the edges of the pastry over the fruit. Using a pastry brush, brush the lightly beaten egg over the pastry. Sprinkle a little extra demerara sugar over the tart.
Bake the crostata over indirect medium-low heat for 40 minutes, or until the pastry is golden.
Remove the crostata from the barbecue and allow to cool for 20 minutes before serving. Top with the orange zest. Garnish with the mint leaves and serve with the cream or ice cream.