Preheat the oven to 350 degrees F. Line 56 mini cupcake cups from 3 (24-cup) mini cupcake or muffin pans or 18 regular-size cupcake or muffin cups from 2 (12-cup) regular-size cupcake or muffin pans with paper cupcake liners.

In a large mixing bowl, combine the flour, sugar, baking soda, and salt. In a second bowl, mix the eggs, buttermilk, and oil. Add the dry ingredients to the wet ingredients. Once the ingredients are mixed, add the lemon zest and lemon juice, and blend until combined. Bake the cupcakes until golden brown and the centers spring back when lightly pressed, 16 to 18 minutes for minis or 22 to 24 minutes for the regular-size cupcakes. Cool the cupcakes in the pans for 5 minutes and then transfer to a wire rack to cool completely.

Increase the oven temperature to 450 degrees F. Transfer the kiwi cream to a pastry bag fitted with a small round tip and fill each cupcake with some of the cream. Transfer the meringue mixture to a separate pastry bag fitted with a large round tip and pipe the meringue on top of each cupcake. Place the cupcakes on baking sheets and bake until lightly browned and cooked through, about 3 to 4 minutes.

In a medium saucepan, melt the butter over medium heat. Add the sugar, eggs, and kiwi mixture. Reduce the heat to medium-low and cook, stirring until it thickens and coats the back of a wooden spoon, about 12 minutes. Set the pan over a large bowl of ice and continue to stir until the mixture has cooled slightly. Strain the mixture into a clean bowl and refrigerate until thickened and well chilled.

In the bowl of an electric stand mixer, combine the egg whites and sugar and whip until the mixture is firm and glossy.