In a small bowl, combine the granulated sugar and lemon zest. Rub the zest into the sugar with your fingertips until the sugar feels slightly damp and very fragrant.

In a large mixing bowl, beat the softened cream cheese and butter with a hand mixer on medium speed until smooth and slightly fluffy, about 2 to 3 minutes.

Add the lemon sugar and brown sugar to the bowl. Beat on medium speed until the mixture looks pale and creamy, scraping down the sides of the bowl as needed.

Add the egg, egg yolk, vanilla extract, and lemon juice. Beat on low to medium speed just until combined and the mixture looks smooth and silky.

In a separate bowl, whisk together the flour, baking powder, baking soda, salt, and poppy seeds until evenly combined.

Add the dry ingredients to the wet ingredients in two additions, mixing on low speed or with a spatula just until no dry streaks of flour remain. The dough will be soft and slightly sticky but should hold its shape.

Cover the bowl and chill the dough in the refrigerator for at least 1 hour and up to 24 hours to firm up and develop flavor.

When ready to bake, preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.

Scoop the chilled dough into balls about 1 1/2 inches (4 cm) across, using about 2 tablespoons of dough per cookie. Roll each portion lightly between your palms to smooth the surface.

If desired, roll the tops of the dough balls in the optional sugar-poppy seed mixture for a bakery-style finish, then place them on the prepared baking sheets, spacing about 2 inches (5 cm) apart.

Bake one sheet at a time for 10 to 13 minutes, until the edges look set and just turning light golden while the centers still look slightly soft and puffed.

Remove the cookies from the oven and let them cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely. The centers will set as they cool, staying soft and cheesecake-like.