Step-by-Step Instructions

1. Preheat your oven to 350°F (175°C). Grease a 9×13 inch baking dish and line with parchment paper.
2. In a large mixing bowl, combine flour, baking powder, salt, and granulated sugar until evenly mixed.
3. Add softened butter, egg, yolk, vanilla extract, and lemon zest. Mix until a soft, crumbly dough forms.
4. Reserve about 1 cup of dough for topping. Press remaining dough into the bottom of the baking dish. Prick the crust with a fork.
5. Bake the crust for 12 minutes, until lightly set and edges begin to turn golden. Let cool slightly.
6. In a saucepan, combine granulated sugar, cornstarch, and lemon juice. Add eggs, yolks, and zest. Whisk until smooth.
7. Cook over medium-low heat, stirring continuously, until thickened (5 to 8 minutes).
8. Remove from heat and stir in butter until completely melted and smooth.
9. Pour lemon filling over the cooled crust. Crumble the reserved dough on top.
10. Bake for an additional 30 to 35 minutes, until the topping is lightly golden.
11. Cool the crostata completely at room temperature, then refrigerate for at least 2 hours.
12. Dust with powdered sugar, and top with lemon slices and mint leaves before serving.