In a medium bowl, whisk together the all-purpose flour and baking powder. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment (or with a handheld mixer and a large bowl), cream the butter, sugar, lemon zest and salt on medium-high speed until pale and fluffy, about 3 minutes.
Add the egg, ricotta and vanilla extract, and mix on medium speed until combined.
Reduce the speed to low and add the flour mixture stirring just until incorporated. The dough will be very soft.
Cover tightly with cling wrap, and refrigerate for at least 2 hours (or up to 3 days).
Preheat the oven to 325°F (165°C) fan assist and line two large baking sheets with parchment paper.
Scoop 2 tablespoons of dough, roll into balls, and place 2 inches (5 cm) apart on the prepared baking sheets.
Bake for 12–14 minutes, until the bottoms are lightly golden but the tops remain pale.
Cool the cookies on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.
In a small bowl, whisk together the powdered sugar and 1 tablespoon of lemon juice until thick but pourable, adding more lemon juice, a few drops at a time, if needed.
Dip the tops of the cookies into the glaze, sprinkle with lemon zest and return to the rack to let the glaze set, about 5 minutes.
Enjoy with a cup of tea! Store leftovers in an airtight container for up to 2 days.