Make the Cookies: The room will fill with a soft dairy scent when you begin combining fats, and you should notice a smoother, silkier texture as the unsalted butter and cream cheese come together. If the mixture seems grainy, keep beating for a bit, scraping sides to ensure even mixing. A common mistake is working with ingredients that are too cold, which prevents proper creaming and leaves lumps.
To the bowl of a stand mixer fitted with the paddle attachment (or large mixing bowl and electric mixer) add the butter, cream cheese, sugar, and beat on medium-high speed until creamed, light, fluffy, and well combined, about 3 minutes.: As you beat, listen for a lighter, airy sound and watch the volume increase to a pale, ribbon like mixture. This aeration helps the cookies rise and stay tender. If you rush this step the dough can be dense, so allow the full time and scrape down the bowl occasionally for even texture.
Stop, scrape down the sides of the bowl, add the egg, lemon extract, and beat on medium-high speed until well combined, about 2 minutes.: After adding the egg and lemon extract , observe the batter smooth out and become cohesive, with a glossy sheen. Smell the citrus lift as the extract integrates. Avoid over mixing here, which may tighten gluten and make the final cookie firmer than intended.
Stop, scrape down the sides of the bowl, and optionally add the yellow food coloring (as many drops as necessary until desired shade is achieved), the lemon zest, and beat on medium speed until combined, about 30 seconds.: The batter will take on color and the tiny flecks of lemon zest will release fragrant oils, adding a fresh citrus perfume. If you skip this brief mixing the zest may not be evenly distributed, creating pockets of flavor rather than a uniform lemon note.
Stop, scrape down the sides of the bowl and add the flour, cornstarch, baking soda, salt, and beat on low speed until just combined, about 1 minute; don’t overmix.: When the dry ingredients enter, you will see the dough thicken and mattify visually. Mixing on low protects the tender structure, preserving a soft crumb. Over mixing will develop gluten and can lead to tougher cookies, so stop as soon as streaks disappear.
Stop, scrape down the sides of the bowl, and using a 2-tablespoon cookie scoop or your hands, form approximately 18 equal-sized mounds of dough, roll into balls, and flatten slightly.: The dough should feel slightly sticky yet manageable; rolling into balls gives each cookie even weight for consistent baking. Flattening ensures even baking and the softbatch texture. Mistakes at this stage include making uneven sizes, which yields uneven baking and some cookies that overbake while others remain underdone.
Place mounds on a large plate or tray, cover with plastic wrap, and refrigerate for at least 3 hours, up to 5 days. Do not bake with unchilled dough because cookies will bake thinner, flatter, and be more prone to spreading.: Refrigeration firms the fats and relaxes gluten, which prevents spreading and creates that soft center. You will notice the dough cools and becomes less sticky. Skipping the chill is the most common error and results in cookies that flatten excessively.
Preheat oven to 350 F, line a baking sheet with a Silpat or spray with cooking spray. Place dough mounds on baking sheet, spaced at least 2 inches apart (I bake 8 cookies per sheet) and bake for about 8 minutes, or until edges have set and tops are just set, even if slightly undercooked, pale, and glossy in the center; don’t overbake or undersides could become too browned. Cookies firm up as they cool.: The oven will give a faint sweet butter aroma and the edges will set first; look for pale tops that still have a glossy sheen. This visual cue ensures a soft center. Overbaking is common and will produce firmer, drier cookies, so remove them when just set.
Allow cookies to cool completely before glazing. I let them cool on the baking sheet and don’t use a rack.: Cooling allows the structure to set and prevents the glaze from running off. You will notice the cookies lose their warm, doughy scent and become slightly firmer to the touch. Glazing too soon will make the icing slide and thin, ruining the finish.
Make the Glaze: The sound when whisking becomes smoother as the confectioners' sugar dissolves, and the mixture will shine as it comes together. Whisk until lump free and silky, adjusting with tiny amounts of lemon juice to reach desired thickness. Adding too much liquid at once can make the glaze overly runny, so add slowly.
To a medium bowl, add the confectioners’ sugar, 2 tablespoons lemon juice, and whisk until smooth and combined. Depending on preference and desired glaze consistency, you may have to play with the sugar and lemon juice ratios slightly.: As you stir, notice the glaze transition from powdery to glossy. Taste a dab for sweetness and acidity; tweak if needed. A common pitfall is impatience with consistency, leading to either dripping or chunks.
Using a small spoon, drizzle about 1 tablespoon of glaze over each cookie, and spread glaze out using the back of the spoon. Repeat until all cookies are glazed.: When you drizzle, watch the glaze pool and then set into a thin skin, that moment indicates correct thickness. Spread gently to avoid disturbing the cookie surface. Overworking the glaze can create streaks that look uneven.
Sprinkle a small pinch of lemon zest over all cookies before the glaze sets and before serving.: The final sprinkle adds a burst of fragrance and visual contrast, tiny flecks of zest bright against the glaze. Do this just before the glaze firms, or the zest may sink or stick inconsistently. Avoid adding zest too early if you want a crisp presentation; it will blur into the glaze.