For Lemon Pastry Cream: Heat milk, cream, and lemon rind in a pot until very hot but not boiling. Remove from heat and let cool to warm. In a separate pot, whisk egg yolks and sugar, then add flour and vanilla. Gradually pour in warm milk/cream, whisking continuously. Cook over medium/low heat until thickened. Remove from heat, transfer to a bowl, cover with plastic wrap (touching the cream), and refrigerate for about 2 hours.

For Crostata Dough: Whisk together flour, salt, sugar, and baking powder in a large bowl. Make a well in the center and add egg, egg yolk, and cubed butter. Mix until dough just starts to come together. Knead on a lightly floured surface until soft, then wrap in plastic and refrigerate for 30-60 minutes.

Preheat oven to 350°F (180°C). Grease and flour a 12-medium muffin tin.

Roll out the dough on a lightly floured surface to 1/8-inch thickness. Cut out circles (approximately 3 1/2 inches/8 1/2 cm). Fit circles into the muffin pan, prick the bottom with a fork, and fill almost to the top with pastry cream.

Wet the rim of each tart, top with another dough circle, and seal by pressing with fingers. Brush the top of each tart with egg wash.

Bake for 30-40 minutes, or until golden brown. Let cool for 15 minutes in the muffin pan, then transfer to a wire rack to cool completely. Dust with powdered sugar before serving.