Prepare the Pan and Oven: Preheat the oven to 350°F (177°C). Line a 12-cup muffin pan with cupcake liners. The recipe makes about 15 cupcakes, so prepare a second batch of liners for the remaining batter.
Combine Dry Ingredients: In a large bowl, whisk together the all-purpose flour, baking powder, and salt until evenly combined. Set the mixture aside.
Cream Butter, Sugar, Lemon Zest: Using a handheld or stand mixer fitted with a paddle attachment, beat the softened butter, granulated sugar, and lemon zest on medium-high speed for about 3 minutes, until the mixture is properly creamed. Scrape down the sides and bottom of the bowl as needed.
Add Eggs and Vanilla: Add the eggs and vanilla extract to the creamed mixture. Beat on medium-high speed for about 1 minute, until everything is well combined, scraping the bowl again as needed.
Finish the Batter: Add the dry ingredients to the wet mixture. Turn the mixer to low speed and slowly pour in the room-temperature milk or buttermilk and fresh lemon juice. Mix only until the ingredients are just combined.
Fold in Blueberries: Add the blueberries that have been tossed in flour. Gently fold them into the batter with a spatula, taking care not to overmix.
Fill the Liners: Spoon or portion the batter into the prepared cupcake liners, filling each one only about two-thirds full to prevent the batter from spilling over during baking.
Bake the Cupcakes: Bake at 350°F (177°C) for 18–21 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. For approximately 30–36 mini cupcakes, bake at the same temperature for about 11–13 minutes.
Cool Completely: Remove the cupcakes from the oven and allow them to cool completely before adding the frosting.
Beat the Frosting Base: In a large bowl, use a handheld or stand mixer fitted with a whisk or paddle attachment to beat the softened cream cheese and butter on medium speed for about 2 minutes, until smooth.
Finish the Frosting: Add the confectioners’ sugar, vanilla extract, and a pinch of salt. Beat on low speed for 30 seconds, then increase to medium-high and continue beating for 2 full minutes. Taste the frosting and add another small pinch of salt if desired.
Chill for Piping: If creating intricate frosting designs, refrigerate the finished frosting for at least 20 minutes before piping.
Frost the Cupcakes: Frost the completely cooled cupcakes using a piping bag fitted with an Ateco #808 piping tip, if desired, or spread the frosting over the cupcakes with a small icing spatula.
Add Garnishes and Set: Decorate with optional lemon slices and extra blueberries. Refrigerate the decorated cupcakes uncovered for at least 20 minutes to help the frosting set before serving.
Store Leftovers: Cover leftover cupcakes and refrigerate for up to 5 days. Use a cupcake carrier if transporting or storing the decorated cupcakes.
