For the brownie: Preheat oven to 350 degrees F. Line bottom of an 8" x 8" square pan with parchment paper. Lightly grease inside of pan with butter.
Place chocolate and butter in a metal bowl set over a saucepan of simmering water. Stir until melted.
Remove from heat.
Add in brown sugar and whisk to combine.
Add in eggs and whisk to combine.
Add in flour, cocoa powder, and salt, and whisk until smooth and combined.
Pour batter into prepared pan and bake for 30-35 minutes until just set.
Place sugar in a medium saucepan.
Add water, making sure sugar is completely wet.
Heat on medium heat until sugar is fully dissolved.Turn heat to high and cook at a boil for about 8 minutes, until mixture reaches 350 degrees F and turns golden brown.
Add in cream and butter - mixture will bubble up violently so be careful. Stir until mixture is well combined.
Add in the puffed rice cereal, sesame seeds, and sesame powder, and stir to combine.
Combine chocolate and cream in a metal bowl set over a saucepan of simmering water. Stir until chocolate is melted and fully mixed with cream.
Add in Grand Marnier and stir to combine.
Pour ganache over caramel layer and let set for about 3 hours or until set.