Preheat the oven to 350 degrees F. Adjust the racks to the upper and lower thirds of the oven. Line two rimmed baking sheets with parchment and set aside.

In a large bowl, whisk together the flour and baking powder. In a separate medium bowl, whisk together the eggs, sugar, butter, vanilla, lemon zest and lemon juice. Add the wet ingredients to the flour mixture and stir with a rubber spatula to combine into a shaggy dough. Turn the mixture onto a lightly flour surface and knead 3 or 4 times to bring together into a smooth dough. Cut the dough into 12 equal pieces. Roll each piece into a 5 inch rope. Form each rope into a circle and place 6 cookies on each of the prepared baking sheets. Bake until the cookies are puffed and deep golden brown, about 10 to 15 minutes. Cool on the trays for 10 minutes before removing to a wire rack to cool completely.

In a medium bowl, whisk together the powdered sugar, water, lemon juice and lemon zest until smooth. Spoon the glaze over the cooled cookies, and add sprinkles if desired. Allow the glaze to harden, and serve.