A creamy surprise awaits in these lime-scented cupcakes.
Preheat oven to 325 degrees. Line two standard muffin tins with paper liners.
In a medium bowl, whisk together flour, baking powder and coarse salt. With an electric mixer on medium-high, cream butter and sugar until pale and fluffy, about 3 minutes. Add eggs, one at a time, beating until each is incorporated and scraping down sides of bowl as needed; beat in zest. Combine buttermilk and remaining 2 tablespoons lime juice. Reduce speed to low, add flour mixture in 3 batches, alternating with buttermilk mixture, and beating until just combined after each. Pour 1/4 cup batter into each tin, firmly tapping pans to level batter.
Bake, rotating pans halfway through, until cupcakes spring back to the touch and a cake tester inserted in center comes out clean, about 25 minutes. Transfer tins to wire racks to cool completely.
Fill a small piping bag fitted with a small plain round tip (such as Ateco #4) with lime curd. Insert tip into center of each cupcake and pipe until cupcake begins to mound on top. Dollop each cupcake with about 2 tablespoons cream cheese frosting, then sprinkle with flaky sea salt and lime zest.