Preheat the oven to 350°F (175°C) and arrange the racks in the upper and lower thirds of the oven. Line 2 baking sheets with parchment paper or silicone baking mats. In a medium bowl, whisk together the flour and baking powder, then set the mixture aside.

In a large mixing bowl, beat the softened butter and cream cheese with an electric mixer until smooth and creamy, about 1 minute. A stand mixer fitted with the paddle attachment may also be used. Add the sugar and continue beating until the mixture becomes pale and fluffy, about 3 minutes.

Add the egg and lemon zest to the creamed mixture and beat until fully incorporated. Gradually mix in the reserved flour mixture, followed by the lemon juice and lemon essence. Continue mixing until a smooth, well-combined dough forms.

Using a small cookie scoop or a tablespoon, portion the dough onto the prepared baking sheets, leaving about 1 1/2 inches between each mound. Lightly flatten the tops by pressing with the bottom of a glass coated in sugar.

Bake until the cookies are set and just lightly golden at the edges, about 10 to 12 minutes.

While the cookies are in the oven, prepare the icing. In a medium bowl, stir together the powdered sugar, lemon zest, and lemon juice until the glaze is smooth and thoroughly blended.

Transfer the baked cookies to cooling racks set over rimmed baking sheets. Allow them to cool slightly, then drizzle each cookie with a scant teaspoon of the lemon icing. Add extra lemon zest on top, if desired.

Serve once the glaze has set.