Ingredients
1/3 cup sugar
2 tablespoons cornstarch
1/4 teaspoon coarse salt
1 1/3 cups plain whole-milk yogurt
2 large egg yolks
2 tablespoons unsalted butter
All-purpose flour, for dusting
14 ounces all-butter puff pastry, such as Dufour, thawed
1/4 cup sugar
2 cups sliced strawberries
1 teaspoon fresh lemon juice
Pinch of salt
1/4 cup heavy cream
Preparation
Pastry cream: In a medium saucepan, whisk together sugar, cornstarch, and salt. Whisk in yogurt, egg yolks, and butter. Cook over medium, stirring with a rubber spatula, until mixture comes to a boil, about 7 minutes. Let boil, stirring, 1 minute. Remove from heat; transfer to a bowl. Cover with plastic wrap, pressing it directly onto surface to prevent skin from forming. Refrigerate at least 2 hours and up to 1 day. Just before using, whisk until smooth.
Tartlets: Preheat oven to 400 degrees with one rack in upper third and one in lower third. Lightly dust work surface and puff-pastry sheet with flour; roll out to slightly thinner than 1/4 inch thick. Sprinkle with 2 tablespoons sugar, pressing and rolling sugar so as much sticks as possible. Trim pastry sheet to a 12-by-9-inch rectangle, then cut into nine 4-by-3-inch rectangles. Score a 1/2-inch border around each rectangle. Score center pieces at 1/2-inch intervals for a decorative top, if desired.
Transfer rectangles to a parchment-lined baking sheet; freeze 15 minutes. Bake on top rack 15 minutes, then transfer to bottom rack; bake until caramelized, about 10 minutes more. Transfer to a wire rack; let cool 10 minutes. Using scissors, cut center of tops away and reserve; let cool.
Meanwhile, combine strawberries, remaining 2 tablespoons sugar, lemon juice, and salt; let stand 10 minutes. Whip heavy cream to soft peaks. Fold whipped cream into pastry cream. Divide among tartlets; top with berries. Serve, with reserved tops.