Preheat the oven to 350°F/180°C. Line 2 cookie sheets with parchment paper or silicone mats and set aside.
In a bowl of a stand mixer fitted with the paddle attachment, cream the butter with the sugar until smooth, light in color and creamy (2-3 minutes).
Add vanilla and egg and mix again until the egg is just incorporated but don’t overmix.
Add in the flour, baking powder, and salt and mix again until just combined. Scrape the sides with a spatula so no dry flour is left. The cookie should pull away from the sides of the bowl (if it doesn’t add ½ cup of flour).
Divide the dough into 4 portions, and roll out each using a rolling pin into ¼ inch thickness. Cut out using a cookie cutter and with the help of a offset spatula transfer to the cookie sheet.
Bake for 8-9 minutes rotating at 6 minutes for even browning (one sheet at a time). Allow to cool on the cookie sheet fo2 5 minutes, then transfer to a wire rack. Cool completely before icing the cookies.
To make the royal icing, in a bowl combine the powdered sugar with meringue powder and water (add the water gradually, start with 6 tablespoons and then add more as needed). Whisk until combined but do not overmix (I learned from my mistake when I over whipped the royal icing in my stand mixer and my cookie turned out dull and lost the nice shine that you get with royal icing). We are looking for 15 seconds consistency for outlining and 8-10 seconds for flooding (which is perfect for this size of cookies, I used 10cm cookie cutter, please find a link on Amazon).
To ice the cookies, divide the royal icing between bowls and add food coloring you’re using (I use Wilton gel colors, and add them with a toothpick) they do not change the consistency of the icing since they’re gel not liquid. I also use Wilton disposable pipping bags, and secure with a small rubber band. You can use a tip or not, but if you use a tip then a coupler is recommended so that the tip is not pushed inside. I use #2 tip to outline and flood the cookies. Outline and flood the cookies first, and then decorate starting from the first cookie you flooded so that it’s set and the decorations are not submerged with the flooding. Allow the icing to set for at least 2 hours at room temp but preferably overnight.
Notes
Store these cookies at room temperature for up to two weeks. You can also freeze the cookies (decorated or not) in a sealed container for up to 3 months.