Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats so the cookies don’t stick and don’t brown too hard on the bottom.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and fine sea salt until well combined. Set aside.

In a large mixing bowl, beat the softened unsalted butter and granulated sugar on medium speed for 2–3 minutes, until light, pale, and fluffy. Use a stand mixer with the paddle attachment or a hand mixer.

Beat in the egg until fully combined, scraping down the bowl as needed. Add the ricotta, vanilla extract, and lemon zest (if using). Mix on medium speed until the mixture looks smooth and creamy; it may look slightly curdled at first, then come together.

Add the flour mixture to the ricotta mixture in two additions, mixing on low speed just until no dry streaks of flour remain. The dough will be thick and sticky, more like a soft muffin batter than a stiff cookie dough.

Using a small cookie scoop (about 1 tablespoon) or two spoons, drop rounded mounds of dough onto the prepared baking sheets, spacing them about 2 inches apart. If the dough is very sticky, lightly dampen the scoop or your fingers with water.

Bake one sheet at a time for 10–13 minutes, until the cookies are puffed, very lightly golden on the bottom, and just set on top. The tops should remain pale and soft; if you gently press one, it should spring back.

Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely. For a pretty, opaque glaze, do not glaze while warm.

In a medium bowl, whisk together the powdered sugar, 2 tablespoons of milk, your choice of vanilla, almond extract, or lemon juice, and a pinch of salt. Add more milk, a teaspoon at a time, until you have a thick but pourable glaze that slowly ribbons off the whisk. If it becomes too thin, whisk in a little more powdered sugar.

Dip the top of each cooled cookie into the glaze, letting excess drip back into the bowl, then place it back on the wire rack. Immediately add sprinkles or nonpareils while the glaze is still wet. Work in batches so the glaze doesn’t dry before the decorations stick. Let the glaze set for 30–45 minutes before stacking or storing.