Preheat oven to 350°F and grease two 8" or 9" cake pans.
In a medium bowl, whisk the flour, baking powder, and salt together.
In a liquid measuring cup combine the buttermilk and Baileys. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar on medium high until light and fluffy - about 2 minutes.
Add eggs one at a time, fully incorporating after each addition. Add in the vanilla extract.
Turn the mixer down to medium and alternate adding the dry ingredients and buttermilk/Baileys mixture, starting and ending with the dry ingredients. Be careful not to over mix!
Distribute the batter into the pans and bake for 25-30 minutes or until a toothpick inserted in the center comes out clean. Let the cakes cool about 10 minutes in the pan. Then transfer them to a wire rack to cool completely.
Baileys Espresso Buttercream
Using a stand mixer fitted with the paddle attachment, cream butter on high – about 2 minutes.
Add in 3 cups of the confectioners sugar and mix until combined.
Add the Baileys and remaining 3 cups of confectioners sugar and beat until combined.
Add the vanilla and espresso powder and beat until light and fluffy – about 3 minutes.
If the frosting is too thick, add more Baileys or add in heavy cream 1 tablespoon at a time until you reach your desired consistency.
Roughly chop the chocolate and place it in a microwave safe bowl. Pour the heavy cream into the same bowl.
Microwave in 30 second intervals, stirring in between each, until the chocolate is completely melted and combined.
Let the ganache cool completely until thick.
Level the tops of the cake layers using a knife or cake leveler.
Place one layer of cake on a turntable or cake stand.
Top it with a thin layer of cooled ganache.
Carefully spread a layer of buttercream on top of the ganache.
Repeat with the next layer(s) of cake.
Coat the outside of your cake with a light layer of frosting, also known as a crumb coat. Then put the cake in the fridge about 30 minutes.
Take the cake out and decorate with remaining frosting as desired.
This recipe can also be made using three 6" cake pans.