1: To make the ice cream, mix all of the ingredients together in a bowl until well combined and very smooth, then churn in an ice-cream machine according to the manufacturer’s instructions. Place the mixture in a freezer container and freeze until needed. Remove from the freezer about 10 minutes before you want to serve it.
2: Next make the pastry. Cream together the butter and sugar. Fold in the flour, powdered bran flakes and salt. Add the eggs and mix to form a paste. Wrap in clingfilm and place in the fridge to rest for at least 1 hour, or up to a day.
3: Preheat the oven to 170°C/Gas mark 3.
4: On a lightly floured surface, roll out the pastry to the thickness of a £1 coin. Use the pastry to line a 24cm loose-bottomed tart tin, gently pressing the pastry all of the way in and letting the excess hang over the sides. Line the inside with baking parchment or several layers of cling film and pour in some ceramic baking beans, uncooked rice or dried pulses to fill the base. Place the tin on a baking sheet and bake for 20-25 minutes. Remove from the oven, take out the parchment and beans and return to the oven for a further 10 minutes until the tart shell is cooked through and dried out. Leave to cool.
5: Lower the oven temperature to 160°C/Gas mark 2 1/2. To make the filling, melt the. Butter in a saucepan over a medium heat until it foams and turns a nutty, golden brown. Whisk in the golden syrup, which will stop the butter from cooking further. Take the pan off the heat, pass the mixture through a fine sieve to remove any solids and set aside.
6: Mix the brioche crumbs in a medium-sized bowl with the butter and syrup mixture. Whisk in the cream, whole eggs, egg yolk and salt, and leave to cool for 10-15 minutes. Pour in the tart case and place on a bakin g sheet in the oven to cook for 25 minutes.
7: Reduce the oven setting to 140°C/gas mark 1 and cook for a further 30 minutes, until the tart is just set – it should still have a little wobble to it in the centre.
8: Remove from the oven and leave to cool. When ready to serve, sprinkle a little flaky sea salt over the top of the tart, trim the top edges, release the ring and place on a serving plate. Serve with the mascarpone ice cream.