Add the butter, sugar, and lemon zest to a large bowl. Beat with an electric mixer on medium-high speed until light and fluffy, about 4-5 minutes. Scrape down the sides and bottom of the bowl as needed.
½ cup butter, 1 cup granulated sugar, 2 teaspoons lemon zest
Add the vanilla and egg, then mix until fully incorporated.
2 teaspoons vanilla extract, 1 egg
Add the ricotta, then mix on medium speed until evenly combined. The mixture may look slightly curdled, which is normal.
1 cup whole-milk ricotta cheese
In a separate bowl, sift together the flour, baking powder, baking soda, and salt.
2 cups all-purpose flour, ½ teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon kosher salt
Add the dry ingredients to the ricotta mixture. Mix on low speed just until no dry streaks of flour remain. Do not overmix. The dough will be very soft and sticky.
Cover the bowl and refrigerate the dough for at least 1 hour or up to 2 days.
Preheat the oven to 350°F. Line two large baking sheets with parchment paper.
Scoop the chilled dough into balls about 1½ tablespoons in size, then place them on the prepared baking sheets about 2 inches apart.
Bake one pan at a time on the center rack for 10-12 minutes, rotating halfway through, until the tops are set and the bottoms are just beginning to turn pale golden. Do not let them brown.
Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.
Make the glaze by whisking together the powdered sugar, lemon juice, and salt until smooth. The glaze should be thick enough to coat the cookies without running completely off. Add more lemon juice, ½ teaspoon at a time, as needed.
1 ½ cups powdered sugar, 3 tablespoons lemon juice, 1 pinch kosher salt
Dip the tops of the fully cooled cookies into the glaze, then allow the excess to drip back into the bowl.
Decorate with sprinkles immediately while the glaze is wet, then place on a wire rack and let them sit until the glaze is completely dry and firm.
rainbow nonpareils or lemon zest
Serve immediately or store in an airtight container for up to 3 days at room temperature or 1 week in the refrigerator.