1. Preheat the oven to 350°F and line a 12-cup muffin pan with paper liners.

2. In a medium bowl, whisk together the flour, baking powder, and salt.

3. In a large bowl, beat the softened butter and granulated sugar until pale and fluffy.

4. Add the eggs one at a time, mixing well after each one.

5. Mix in the lemon zest, fresh lemon juice, and vanilla extract.

6. Add the dry ingredients in batches, alternating with the milk, and mix just until combined.

7. Divide the batter evenly among the cupcake liners, filling each about two-thirds full.

8. Bake for 18 to 22 minutes, or until a toothpick inserted into the center comes out clean.

9. Let the cupcakes cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.

10. For the buttercream, beat the softened butter until creamy.

11. Gradually mix in the powdered sugar, then add the lemon zest, fresh lemon juice, and heavy cream.

12. Beat until light and fluffy, adjusting with a little more cream or powdered sugar if needed.

13. Pipe or spread the lemon buttercream onto the cooled cupcakes.

14. Garnish with extra lemon zest if desired and serve.