Prep: Preheat the oven to 400°F (200°C) and grease two 8½-inch (22 cm) cake pans.
Whip the Eggs and Sugar: Add the eggs, brown sugar, granulated sugar, and salt to a mixing bowl. Beat until the mixture becomes pale, airy, and approximately doubles in volume.
Add the Liquids: Pour in the oil, vanilla, and Baileys. Mix until evenly incorporated.
Combine the Dry Ingredients: In a separate bowl, mix the flour, baking powder, and ground walnuts.
Make the Batter: Gradually fold the dry ingredients into the wet mixture in portions until everything is combined. Avoid overmixing so you keep some of the air in the batter.
Fill the Pans: Divide the batter evenly between the two prepared 22 cm cake pans.
Bake: Bake at 400°F (200°C) for about 20 minutes, or until the cakes are baked through and a toothpick inserted into the center comes out clean.
Cool: Let the cake layers cool completely before adding the filling.