01 - Preheat your oven to 350°F (175°C). Line a standard 12-cup muffin tin with paper liners, ensuring it's ready for baking.
02 - In a medium mixing bowl, whisk together the all-purpose flour, baking powder, and salt until they are thoroughly combined. Set this dry mixture aside.
03 - In a large mixing bowl, using an electric mixer, beat the softened unsalted butter and granulated sugar together until the mixture becomes light, fluffy, and pale in color, which typically takes about 2 to 3 minutes.
04 - Add the large eggs to the creamed butter mixture one at a time, beating well after each addition to fully incorporate. Stir in the vanilla extract until just combined.
05 - In a small bowl or measuring cup, combine the alcohol-free Irish cream liqueur and whole milk, mixing gently.
06 - With your mixer set to a low speed, gradually add the reserved flour mixture to the wet ingredients in three separate additions. Alternate these additions with the Irish cream and milk mixture, beginning and ending with the flour mixture. Mix only until the ingredients are just combined and no streaks of flour remain, being careful not to overmix.
07 - Distribute the cupcake batter evenly among the prepared 12 muffin liners, filling each approximately two-thirds full.
08 - Bake the cupcakes for 16 to 18 minutes, or until a wooden toothpick inserted into the center of a cupcake comes out clean. Allow the cupcakes to cool in the muffin tin for 5 minutes before carefully transferring them to a wire rack to cool completely. Ensure they are fully cooled before frosting.
09 - For the buttercream, beat the softened unsalted butter in a medium bowl with an electric mixer on medium speed until it is creamy and smooth, about 2 minutes. Gradually add the sifted powdered sugar, beating until the mixture is smooth. Incorporate the alcohol-free Irish cream liqueur, vanilla extract, and a pinch of salt. Continue to beat for 1 to 2 minutes until the buttercream is light and fluffy.
10 - Once the cupcakes have cooled completely, generously frost them with the prepared Irish cream buttercream. You can use a piping bag for a decorative finish or a spatula for a classic swirl.