Beat softened butter with caster sugar and cinnamon until combined. Set aside.
Whisk eggs, milk, cream, sugar, vanilla, cinnamon and salt in a shallow dish.
Dip brioche slices in custard, 30 seconds each side, pressing gently so the bread absorbs. Dust one side with caster sugar.
Heat a large frypan over medium heat. Melt a generous knob of butter.
Cook brioche, sugared side down first, 2-3 minutes until caramelised and golden. Flip, cook another 2 minutes. Work in batches, keeping cooked pieces warm.
Serve two slices per person topped with a pat of cinnamon butter, a generous pour of maple syrup, fresh berries, and a snow of icing sugar.