Heat the oven to 350 degrees. Line muffin pans with 18-20 paper liners. Whisk the flour, baking powder and salt together in a bowl; set aside.
Combine the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment. Beat on low speed until well mixed. Increase the speed to medium; beat until mixture is very light and pale in color, about 5 minutes. Beat in the vanilla.
Beat in the eggs one at a time, beating smooth after each addition. Beat in the melted chocolate. Scrape the bowl and beater with a spatula.
Restart the mixer on low. Add a quarter of the flour mixture; beat until absorbed. Increase speed to medium-low; beat in 1/4 cup milk.
Repeat step 4, including the change of speed, two more times.
Stop and scrape; beat in the remaining flour mixture. Scrape again. Increase the speed to medium; beat 3 minutes.
Divide the batter among the lined pans, filling the cups to the top. Bake 15-20 minutes. Cool before proceeding with parfait. (Enjoy remaining cupcakes as you like.)