Place the toasted breadcrumbs, butter and caster sugar into a food processor and blend to mix.
Whisk together the cream cheese, icing sugar, orange and lemon juice and zest in a large bowl.
Grease the inside of a tall 7cm/3in chefs' ring, and place into the centre of a plate. Spoon in the breadcrumb mixture and press down until the ring is half-filled with biscuit base.
Spoon the cream cheese mixture into the ring and smooth the top with a palette knife.
To serve, carefully remove the chefs' ring and garnish with a mint sprig.