In the bowl of a stand mixer fitted with a paddle attachment (or with a medium bowl and a handheld electric mixer), beat the ricotta, butter, granulated sugar, and lemon zest on medium-high speed until light and fluffy, about 5 minutes.

Beat in the egg and vanilla extract until combined, scraping down the sides of the bowl a few times to ensure even mixing.

In a small bowl, whisk together the flour, baking powder, and salt, then turn the mixer to low and gradually beat in the flour mixture until just combined.

Transfer to an airtight container and refrigerate until firm, about 2 hours or up to 2 days.

When ready to bake, preheat the oven to 350°F (180°C) and line 2 baking sheets with parchment paper.

Roll 1½-tablespoon portions of dough into balls and place about 2 inches (5 cm) apart on the prepared baking sheets.

Bake for 12-14 minutes, rotating the baking sheets halfway through (the tops will remain pale, but the bottoms can get quite dark, so watch carefully.)

Let the cookies rest on the baking sheets for a few minutes before transferring to a wire rack to cool completely.

In a small bowl, mix the powdered sugar with the melted butter, lemon juice, vanilla extract, and 2 tablespoons milk until smooth. (The glaze should be thick but pourable. If you want a thinner glaze, add the extra tablespoon of milk a little at a time until the desired thickness is achieved.) Cover and set aside until the cookies are completely cool.

Dip the tops of the cookies into the glaze, then return them to the wire rack and immediately add the sprinkles, if using, before the glaze dries.

Store in an airtight container at room temperature for up to 3 days.