Whisk the flour, baking powder, and salt together in a medium bowl. Set aside.

In a large bowl using a handheld or a stand mixer fitted with a paddle attachment, beat the butter and sugar together on high speed until completely smooth and creamy, about 3 minutes. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Add the egg, vanilla extract, lemon extract, and lemon zest and beat on high speed until combined, about 1 minute. Scrape down the sides and up the bottom of the bowl and beat again as needed to combine.

Add the dry ingredients to the wet ingredients and mix on low speed until combined. Dough will be a bit soft. If the dough seems too soft and sticky for rolling, add 1 more Tablespoon of flour.

Divide the dough into 2 equal parts. Place each portion onto a piece of lightly floured parchment paper or a lightly floured silicone baking mat. With a lightly floured rolling pin, roll the dough out to about 1/4-inch thickness. Use more flour if the dough seems too sticky. The rolled-out dough can be any shape, as long as it is evenly 1/4-inch thick.

Lightly dust one of the rolled-out dough portions with flour. Place a piece of parchment paper on top. (This prevents sticking.) Place the 2nd rolled-out dough on top. Cover with plastic wrap or aluminum foil, then refrigerate for at least 1–2 hours and up to 2 days.

Once chilled, preheat oven to 350°F (177°C). Line 2 or 3 large baking sheets with parchment paper or silicone baking mats. Carefully remove the top dough piece from the refrigerator. If it’s sticking to the bottom, run your hand under it to help remove it. Using a cookie cutter, cut the dough into shapes. I used this flower cookie cutter for the fireworks cookies. For the pictured little stars (that just have flooded icing on them), I used a small star from this set.

Re-roll the remaining dough and continue cutting until all is used. Repeat with 2nd piece of dough. (Note: It doesn’t seem like a lot of dough, but you get a lot of cookies from the dough scraps you re-roll.)

Arrange cookies on baking sheets 3 inches apart. Bake for 11–12 minutes or until lightly browned around the edges. If your oven has hot spots, rotate the baking sheets halfway through bake time. Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely before decorating.

Watch the video of the icing below so you get an idea of what the final consistency should be. Pour confectioners’ sugar, meringue powder, and 9 Tablespoons of water into a large bowl. Using a hand mixer or a stand mixer fitted with a whisk attachment, beat icing ingredients together on high speed for 1.5 – 2 minutes. When lifting the whisk up off the icing, the icing should drizzle down and smooth out within 5-10 seconds. If it’s too thick, beat in more water 1 Tablespoon at a time. I usually need 10 Tablespoons but on particularly dry days, I use up to 12-14 Tablespoons. Keep in mind that the longer you beat the royal icing, the thicker it becomes. If your royal icing is too thin, just keep beating it to introduce more air OR you can add more sifted confectioners’ sugar.

Divide the icing up into separate bowls, depending on how many colors of icing you’d like. Stir in gel food coloring, and then spoon the icings into piping bags fitted with piping tip #2 or piping tip #3. Pipe curved lines from the middle of the cookie to the edges. (I make the “middle” a little more off center to look more like a firework, see photos.) If you want to add sprinkles like the pictured cookies, I piped every other line, dipped the cookie (with wet icing) into sparkling sugar sprinkles, and then piped the rest of the lines. You can also add little star sprinkles to the fireworks cookies, and I used the stars from this sprinkle mix. Pipe a little dot of icing, then adhere the star sprinkle to it.

For the pictured plain star-shaped cookies, I suggest Wilton piping tip #3 or Wilton piping tip #4. Pipe a border around the cookies and then flood the center with icing. Feel free to dip into sprinkles.

Icing completely dries in about 2 hours at room temperature. No need to cover the decorated cookies as you wait for the icing to set. If it’s helpful, decorate the cookies directly on a baking sheet so you can place the entire baking sheet in the refrigerator to help speed up the icing setting.

Enjoy cookies right away or wait until the icing sets to serve them. Once the icing has set, these cookies are great for gifting or for sending. Plain or decorated cookies stay soft for about 5 days when covered tightly at room temperature. For longer storage, cover and refrigerate for up to 10 days.