PASSION FRUIT-FILLED CUPCAKES

Steps:

• Make the passion fruit curd: In a medium saucepan, whisk together sugar and egg yolks; whisk in passion fruit puree and salt. Add butter and place pan over medium-high heat. Cook, whisking constantly, until butter has melted, mixture is thick enough to coat the back of a spoon, and small bubbles form around the edge of the pan, about 5 minutes.
• Remove pan from heat while continuing to whisk. Strain curd through a fine-mesh sieve into a bowl. Cover with plastic wrap, pressing directly onto the surface of the curd to prevent a skin from forming. Refrigerate until chilled, at least 2 hours. Rinse and dry saucepan.
• Make the cupcakes: Preheat oven to 350 degrees. Line two standard 12-cup muffin pans with paper liners. In a medium bowl, sift together flours, baking powder, and salt.
• In the bowl of an electric mixer fitted with the paddle attachment, beat sugar and butter, scraping down the sides as needed, until light and fluffy, 3 to 4 minutes. Beat in eggs, one at a time, then beat in vanilla. With the mixer on low speed, add flour mixture in three additions, alternating with the milk and beginning and ending with the flour mixture; beat until combined after each addition.
• Divide the batter evenly between the prepared cups, filling each about two-thirds full. Bake, rotating pans halfway through, until cupcakes are golden brown and a cake tester inserted in a center comes out clean, about 20 minutes. Transfer pans to a wire rack to cool. Invert cupcakes onto the rack; reinvert and let cool completely.
• Make the meringue buttercream: While cupcakes are baking, fill the reserved saucepan with about 2 inches water and bring to a simmer. Combine sugar, egg whites, and salt in the heatproof bowl of a standing mixer. Set bowl over (not in) simmering water, and whisk until mixture is warm to the touch and sugar dissolves, 2 to 3 minutes. (Test by rubbing between your fingers; the mixture should feel smooth.)
• Attach bowl to standing mixer fitted with whisk attachment, and beat on low speed until foamy. Add cream of tartar, and beat on medium-high speed until stiff, glossy peaks form and mixture is cooled completely, about 10 minutes.
• Reduce speed to medium-low; add butter, 2 tablespoons at a time, beating to incorporate fully after each addition. (Buttercream may appear curdled at this point; it will become smooth again with continued beating.) Beat in vanilla. Switch to paddle attachment. Beat on lowest speed, 3 to 5 minutes. Transfer to a pastry bag fitted with a large star tip.
• Assemble the cupcakes: Using an apple corer, make a small hole in the top of each cupcake, reserving tops. Fill each cupcake with about 1 tablespoon chilled passion fruit curd. Replace reserved tops, then pipe frosting onto cupcakes, as desired.