Preheat the oven to 350° and line a 12-cup muffin pan with cupcake liners; set aside.
In a large bowl, whisk together the flour, cocoa powder, baking soda, and salt until well combined and then set aside. Whisk eggs, granulated sugar, brown sugar, oil, and vanilla until smooth and with no lumps. Pour half of the wet mixture and half of the buttermilk into the dry ingredients and gently whisk. Repeat with the rest of the wet mixture and buttermilk and whisk into the dry ingredients just until combined. Do not overmix.
Spoon batter into cupcake liners to fill only halfway. Bake for 18-21 minutes, or until a toothpick comes out clean. Place cupcakes on a wire rack to cool.
Baileys Irish Cream Frosting
In a large bowl using a hand mixer or a stand mixer fitted with a paddle attachment, cream the room temperature butter and cream cheese until fluffy and smooth (about 2 minutes). Scrape down bowl when necessary. Add powdered sugar and while the mixer is on low gradually pour half of Bailey’s Irish Cream. Cream until all the ingredints are fully combined and frosting is thick and fluffy. (about 1 minute) If the frosting seems too thick add the rest or until it is at the right consistency.
Pipe frosting onto cooled cupcakes with whatever way you prefer. If piping, for reference I used a Wilton 1M tip.
Optional: Chocolate Drizzle
Melt 2 ounces of baking chocolate in a small microave save bowl. Pour melted chocolate into a zip lock bag. Cut a small bit off one of the bottom corners of the bag and drizzle back and forth onto your cupcakes.