Heat the oven to 180C/fan 160C/gas 4. Unravel the Jus-Rol™ Shortcrust Pastry Sheet and use to line a 20cm tart tin. Press into the sides of the tin and loosely cut around the edges, leaving a little overhanging. Line the pastry with a scrunched-up piece of baking parchment, and fill with raw rice or baking beans. Bake for 15 mins, remove the paper and bake for another 5-10 mins until dry.
While the pastry is cooking, put the butter and chocolate into a heatproof bowl set over a pan of just-simmering water and melt together, stirring often. When melted, remove from the heat and leave to cool slightly. Add a pinch of salt if your butter is unsalted.
Whisk together the eggs and sugars briefly in a bowl until combined, then stir in the melted chocolate and butter. Sieve over the flour and fold in until just combined. Stir in the orange juice and zest.
Trim the edges of the pastry tart with a serrated knife to neaten, and spoon the brownie mixture into the middle. Smooth over with the back of a spoon or spatula, and bake for a further 30-35 mins until the top forms a crust, and the filling is no longer wet but slightly wobbly.
Leave to cool for 15 mins before removing from the tin if serving warm, or serve at room temperature. Serve with a dollop of crème fraîche, and some more orange zest grated over. Keeps for 3 days in an airtight container.