In a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, cream together the softened unsalted butter and granulated sugar on medium speed until light and fluffy, about 3-4 minutes.

Beat in the large egg, vanilla extract, and lemon zest until well combined, scraping down the sides of the bowl as needed.

In a separate medium bowl, whisk together the sifted all-purpose flour, baking powder, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined and a soft dough forms. Be careful not to overmix.

Divide the dough into two equal portions, flatten each into a disc, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes (or up to 2 days). Chilling prevents the cookies from spreading too much during baking.

Preheat oven to 375°F (190°C). Line two large baking sheets with parchment paper.

On a lightly floured surface, roll out one disc of chilled dough to about ¼-inch thickness. Use Easter-themed cookie cutters to cut out desired shapes.

Carefully transfer the cut-out cookies to the prepared baking sheets, leaving about 1 inch between them. Gather any dough scraps, gently re-roll, and cut more cookies until all dough from that disc is used.

Bake for 10-12 minutes, or until the edges are lightly golden and the centers are set. Baking time may vary depending on cookie size and thickness.

Let the cookies cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely. Repeat with the second dough disc. Ensure cookies are completely cool before frosting.

In a medium bowl, combine the sifted powdered sugar, milk (or water), light corn syrup (if using), and vanilla extract.

Whisk until smooth and lump-free. The consistency should be pourable but still thick enough to hold a shape when drizzled. Add more milk/water by the teaspoon if too thick, or more powdered sugar if too thin, to reach your desired consistency for outlining and flooding.

Divide the icing into several small bowls, one for each color you plan to use. Add a few drops of gel food coloring to each bowl and mix until desired shades are achieved.

Transfer the colored icings to piping bags fitted with small round tips (or use a Ziploc bag with a tiny corner snipped off for a makeshift piping bag).

First, outline the border of each cooled cookie with a slightly thicker consistency of icing. Let it set for 5-10 minutes.

Then, "flood" the inside of the outlined area with a slightly thinner icing, using a small spoon or toothpick to gently spread it evenly to the edges.

Allow the flooded icing base layer to set for at least 30-60 minutes before adding any details, or ideally, let them dry completely for several hours (or overnight) to prevent smudging.

Once the base layer is dry, use contrasting colors to add details like dots, lines, zigzags, or sprinkles to your Easter cookies. Let all decorations dry completely before stacking or storing.