How to Make It
Prepare the Cake: Preheat oven to 350°F. Spray a 12-cup Bundt pan with cooking spray, and dust with cocoa, tapping out the excess.
Heat beer in a medium saucepan over medium-high until boiling. Reduce heat to medium, and simmer until beer is reduced to 3/4 cup, about 15 minutes. While beer reduces, whisk together flour, baking soda, and salt in a medium bowl. Set aside.
Whisk butter, semisweet chocolate, and molasses into reduced beer until butter and chocolate melt. Set aside.
Beat together granulated sugar and eggs with an electric mixer on medium-high speed until fluffy, 2 to 3 minutes. Stir in chocolate mixture and sour cream. Gradually add flour mixture, beating on low speed until just combined.
Pour batter into prepared Bundt pan, and bake in preheated oven until a toothpick inserted into the center comes out clean, 50 to 55 minutes. Let cake cool in pan 30 minutes, then invert onto a serving platter. Cool another 30 minutes.
Prepare the Chocolate Glaze: combine Irish cream, heavy cream, and corn syrup in a glass measuring cup; heat in a microwave on HIGH for 30 to 45 seconds. Place bittersweet chocolate in a small bowl, and pour warm cream mixture over it; let stand 1 minute, then gently stir until smooth. Once mixture is smooth, increase speed of stirring until chocolate mixture is emulsified and glossy; set aside.
Prepare the Whiskey Drizzle: whisk together powdered sugar and whiskey in a medium bowl until smooth, and spoon into a piping bag or a ziplock plastic bag with a corner snipped off.
When cake is cool, spoon Chocolate Glaze over entire cake, allowing glaze to drip down sides of cake. Let stand 20 minutes at room temperature, or chill 10 minutes. When glaze has set, drizzle cake with Whiskey Drizzle. Let stand a few minutes before slicing cake.