Preheat the oven to 350°F/180°C, or 160°C fan oven. Prepare a cookie sheet by lining it with parchment paper or silicone mat 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 incorporated but don’t over whip (the longer you whip the egg, it can souffle up and the cookies will rise and you don’t want that).
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 for 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 .
Divide icing into small bowls. Add food coloring with a toothpick to get desired shades. Add water as needed to get the royal icing to the proper consistency. To ice and flood cookies you'll need a 15-second consistency icing for outlining and details and an 8-10 second consistency for filling. (see Note 1)
Add the icing to piping bags fitted with couplers and #2 round tips, or cut a small hole in the tip of the piping bag.
Outline and flood the cookies first to create a solid background. Decorate with details after the first layer has mostly dried so that the details will stand up.
Allow the icing to set for at least 2 hours at room temperature, and preferrably overnight before storing.
Notes
To test the consistency of royal icing, use a spoon to lift some out of the bowl and drizzle it back in. Count the seconds that it takes for that line of icing to disappear. Add water drop by drop to thin the icing out. A little bit goes a long way.
This cookie recipe will make approximately 36 cookies using a 4 inch (10cm) egg shaped cookie cutter. You may get more or fewer cookies depending on the shapes that you make.
Avoid overmixing the royal icing. If you add too much air to it, it becomes dull.
To Store: Decorated Easter cookies with royal icing can be stored at room temperature in an airtight container for up to 2 weeks. The icing keeps the cookies from drying out. Undecorated cookies will stay fresh for up to 1 week if you'd like to make the cookies one day and then decorate them later.
To Freeze: Seal the cookies in an airtight container with a layer of parchment or wax paper between layers. Decorated and undecorated sugar cookies will keep in the freezer for up to 3 months.