Begin by preheating the oven to 350°F. Place cupcake liners in baking pans.
Add 1/4 cup of warm water, 1/2 cup of Baileys, 1/3 cup vegetable oil, 1/3 cup melted and cooled chocolate chips, and 2 large eggs into a large bowl.
Whisk together until smooth.
Sift the dry ingredients into the wet ingredients (3/4 cup flour, 3/4 cup sugar, 1/2 tsp baking soda, 1/2 tsp salt, and 1/3 cup baking cocoa) and stir until just combined.
Scrape the sides and bottom of the bowl as needed with a spatula.
Add in 1 tsp vinegar and 1 tsp vanilla extract, and mix until the batter is smooth - it will be a bit thick!
Fill cupcake liners 3/4 full, and bake for about 18 minutes, or until a toothpick comes out with moist crumbs.
Allow cupcakes to cool in pans for 10 minutes, then remove and place in the freezer for 15 minutes (to accelerate the cooling process).