Preheat oven to 350°F. Line a baking sheet with parchment paper.
Make the wet mixture: In a large bowl, cream together butter, granulated sugar, lemon zest, vanilla, and salt using a hand or stand mixer on medium speed until light and fluffy, 2–3 minutes.
Add lemon juice and egg yolk. Beat until fully incorporated.
Combine dry ingredients: In a separate bowl, whisk together baking powder, cornstarch, and flour.
Add dry mixture to wet ingredients and mix on low speed until just combined. Use a spatula to bring the dough together, being careful not to overmix.
Cover and chill dough in the refrigerator for at least 1 hour. This helps prevent spreading.
Shape cookies: Scoop heaping teaspoons of dough (about 1 tablespoon each) and roll into balls. Place on the prepared baking sheet, spacing them about 2 inches apart.
Bake for 10–12 minutes, or until edges are just beginning to turn golden and centers look slightly puffed. Do not overbake.
Let cookies cool on the sheet for 5 minutes, then transfer to a wire rack to cool completely.
Once cool, toss cookies in powdered sugar to coat. Store in an airtight container.
Notes
Use room temperature butter and yolk for the best creaming texture.
Forgot to soften the butter? Microwave water in a glass, pour it out, and invert the warm glass over your butter for a quick fix.
Don’t skip chilling the dough—this helps the cookies keep their shape.
Sift powdered sugar if it’s clumpy before coating the cookies.
Cookies may look underdone—trust the timing and let them finish setting on the baking sheet.
Add more lemon zest for a punchier citrus flavor, or roll twice in sugar for extra coating.
STORAGE
Store baked lemon coolers in an airtight container at room temperature for up to 5 days—though, let’s be real, they'll probably disappear within a day!
Unbaked cookie dough balls freeze well for up to 3 months. Wrap them tightly in plastic wrap, place in freezer-safe containers, and when you're ready to bake, thaw overnight in the fridge and bake as usual.
To freeze baked cookies, let them cool completely first. Store them in freezer-safe containers for up to 2 months. Thaw cookies at room temperature, then enjoy.