Preheat oven to 350 F. Liberally spray a 10-inch (12-cup) bundt pan with Pam or some other cooking oil spray.
Set aside 1/2 cup of the flour.
In a large mixing bowl, sift together the remaining dry ingredients -- 2 cups flour, baking powder, baking soda, and salt.
In a separate bowl, whisk together the buttermilk, granulated sugar, oil, eggs, and vanilla.
Add the wet ingredients to the flour mixture. Beat with a wire whisk until just combined, scraping down the bottom of the bowl as needed.
To make the chocolate cake batter: In a medium bowl, combine the cocoa powder and espresso powder. Add half of the buttermilk mixture to the cocoa mixture, stirring until smooth. Set aside.
To make the vanilla cake batter: Add the reserved half cup of flour into the remaining buttermilk mixture, whisking until just combined.
Spoon half of the vanilla batter evenly in the bottom of the pan. Carefully spoon half of the chocolate mixture on top of the cake batter. Add remaining batter, alternating between vanilla and chocolate. Run a butter knife gently through the batter to combine the cake layers just slightly for the chocolate swirl marbling effect.
Bake in preheated oven for 30 to 35 minutes or until a toothpick inserted near the center comes out clean.
Cool on a wire rack for 10 minutes, then immediately remove the cake from the pan.
Place the cake on a wire rack set over a sheet of parchment paper. Using a long wooden skewer, poke cake in several places, all the way through to the bottom of the cake.
In a small bowl, stir together the coffee drizzle ingredients.
Slowly pour the coffee drizzle evenly over the top of the cake.
Cool completely. Decorate by sifting the powdered sugar and cocoa over the top, if desired.