Preheat oven to 170C/150C fan-forced. Grease an 18cm x 28cm slice pan. Line base and sides with baking paper, extending paper 2cm above all sides. Place dark chocolate and butter in a medium saucepan over medium heat. Cook, stirring occasionally, for 4 to 5 minutes or until mixture is melted and smooth. Remove from heat. Cool for 10 minutes.The easy way to line a square cake tin with baking paper.
Meanwhile, make Cheesecake Swirl Using an electric mixer, beat cream cheese, sugar and vanilla until light and fluffy. Add egg. Beat until combined.
Whisk sugar into chocolate mixture. Add eggs, 1 at a time, whisking until combined after each addition. Stir in flours. Spoon 1⁄2 the brownie mixture into prepared pan, spreading to cover base. Drop spoonfuls of remaining brownie and cheesecake mixtures, alternating, on top of brownie mixture in pan. Run a butterknife through the mixtures, swirling to create a marbled effect. Press Baci chocolates into mixture. Bake for 45 minutes or until top is firm to touch. Cool completely in pan. Serve.