Adjust oven rack to middle position and preheat oven to 325℉. Grease a 9-inch springform pan.
Combine chocolate and butter into a bowl and microwave at 50% power, stirring occasionally, until melted, 2-4 minutes. Let cool for 5 minutes.
Whisk sugar, eggs, vanilla, baking powder, and salt together in a medium bowl until combined. Whisk in chocolate mixture until smooth. Stir in flour until no streaks remain. Transfer batter to prepared pan and smooth to the edges. Bake for 22-27 minutes or until a toothpick inserted in the center of the pan comes out with a few crumbs attached. Transfer pan to a wire rack to cool completely.
For the Filling and Top Layer
Combine 1 ½ teaspoons of the gelatin and water in a small bowl and let stand until gelatin softens, about 5 minutes. Place the white chocolate in a large bowl. Heat the Bailey's and espresso powder in a small saucepan over medium heat until just simmering. Pour Bailey's mixture over the white chocolate, add the gelatin mixture, and whisk until melted; let cool slightly, about 10 minutes. Using a stand mixer fitted with the whisk attachment or hand-held mixer, whip cream on medium speed until soft peaks form, about 3 minutes. Whisk one-third of whipped cream into the white chocolate mixture. Using a rubber spatula, fold in the remaining cream. Spread evenly over the cooled brownie layer all the way to the edges of the pan. Refrigerate until set, about 2 hours.
Combine the orange juice, Grand Marnier, and remaining 1 ½ teaspoons of gelatin in a small saucepan and cook over medium high heat, stirring frequently, until just simmering. Transfer to a 2-cup measuring cup and let cool completely, about 1 hour. Slowly pour juice mixture over cake and refrigerate until set, about 1 hour. Run a thin knife between cake and side of the pan; remove springform side. Transfer cake to serving platter and garnish with chocolate curls. Serve. Cake can be made and kept refrigerated three days in advance. Enjoy!
Notes
The alcohol in the recipe is cooked out. If you don't keep these liqueurs around, just pick up a few mini bottles at the store.