In a large mixing bowl, whisk together flour and salt until well combined. In a separate bowl, beat egg with olive oil and sugar until frothy. Gradually mix in the flour mixture until a dough forms. Knead the dough on a floured surface until smooth and elastic, about 5 minutes. Wrap the dough in plastic wrap and refrigerate for at least 1 hour.

While the pastry chills, prepare the ricotta filling. In a bowl, whip the egg yolks with sugar until light and fluffy. Stir in lemon zest, ricotta cheese, and vanilla extract until well blended. In another bowl, beat the egg whites with lemon juice until stiff peaks form. Carefully fold the egg whites into the ricotta mixture until just combined.

Preheat your oven to 350°F (175°C) and grease a muffin pan. Roll out the chilled pastry dough on a floured surface until thin, then cut into squares. Place each square into the muffin cups, pressing gently to form a base. Fill each pastry shell with a spoonful of ricotta filling, leaving a little space at the top. Fold the corners of the dough over the filling.

Place the muffin pan in the preheated oven and bake the pastries for 30 minutes. Reduce the temperature to 325°F (160°C) and continue baking for an additional 15-20 minutes until golden brown.

Remove the pastries from the oven and allow to cool in the pan for about 10 minutes. Transfer to a wire rack to cool completely. Dust with icing sugar before serving.