Preheat your oven to 350°F (175°C) and line a cupcake tray with paper liners.

In a medium bowl, whisk together cake flour, baking powder, and salt to eliminate lumps; set aside.

In a large bowl, cream the unsalted butter and granulated sugar using a hand or stand mixer until light and fluffy, about 1 minute. Beat in eggs, vanilla extract, and lemon zest until fully blended and smooth.

In a small bowl, combine the milk with lemon juice; set aside for a few minutes.

Gradually incorporate half the dry ingredients into the butter mixture, stirring gently. Follow by adding half the milk mixture, mixing until just combined. Repeat the process with the remaining dry and wet ingredients, ensuring everything is just mixed and smooth.

Evenly distribute the batter among the prepared cupcake liners, filling each about halfway. Bake for 17-19 minutes, or until the centers spring back when lightly touched. If an indentation remains, bake for a few more minutes.

Allow cupcakes to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.

In a large mixing bowl, beat room temperature butter and cream cheese until smooth and creamy, about 1 minute.

Gradually add confectioner's sugar, 1 cup at a time, mixing on low speed until well incorporated. Then whip the mixture on high speed for 2-3 minutes, achieving a fluffy texture.

Blend in vanilla extract, lemon juice, and lemon zest, beating for an additional 1-2 minutes until light and airy.

Pipe or spread the frosting generously onto the cooled cupcakes, and serve immediately.