Passion Fruit-Filled Cupcakes

Ingredients

• 4 1⁄4 cups sugar
• 4 large eggs, plus 8 large egg yolks and 6 large egg whites
• ⅔ cup frozen passion fruit puree, defrosted
• ¾ teaspoon plus a pinch salt
• 1 1⁄4 sticks (10 tablespoons) unsalted butter, cut into pieces, plus 2 sticks (1 cup), whole, and 4 sticks (2 cups), cut into tablespoons, room temperature
• 1 ½ cups all-purpose flour
• 1 ½ cups cake flour (not self-rising)
• 1 tablespoon baking powder
• 3 teaspoons pure vanilla extract
• 1 1⁄4 cups whole milk
• 1⁄4 teaspoon cream of tartar

Instructions

1. 1
   In a medium saucepan, whisk together 1 cup sugar and egg yolks; whisk in passion fruit puree and 1/4 teaspoon salt. Add 10 tablespoons 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.
2. 2
   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.
3. 3
   Meanwhile, 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 1/2 teaspoon salt.
4. 4
   In the bowl of an electric mixer fitted with the paddle attachment, beat 1 3/4 cups sugar and 1 cup butter, scraping down the sides as needed, until light and fluffy, 3 to 4 minutes. Beat in 4 eggs, one at a time, then beat in 2 teaspoons vanilla. With the mixer on low speed, add the flour mixture in three additions, alternating with the milk and beginning and ending with the flour mixture; beat until combined after each addition.
5. 5
   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.
6. 6
   While the cupcakes are baking, make the meringue buttercream: Fill the reserved saucepan with about 2 inches water and bring to a simmer. Combine the remaining 1 1/2 cups sugar, egg whites, and pinch of 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.)
7. 7
   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.
8. 8
   Reduce speed to medium-low; add remaining 2 cups 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 remaining 1 teaspoon vanilla. Switch to paddle attachment. Beat on lowest speed, 3 to 5 minutes.
9. 9
   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.
10. 10
    Transfer buttercream to a pastry bag fitted with a large star tip. Pipe onto cupcakes, as desired.