In a medium mixing bowl, use an electric mixer to beat softened butter until creamy. Add granulated sugar and beat until combined.
Add in the egg and vanilla extract. Beat until combined.
Add in the almond flour, baking powder, and salt. Beat on low speed until it forms a soft dough.
Turn the dough out onto a sheet of plastic wrap. Use your hands to press the dough into a flattened disc shape. Wrap with plastic wrap and chill in the fridge for 1 hour.
Preheat oven to 350°F and line a baking sheet with parchment paper. Set aside.
Place the chilled dough on a well-floured surface. Roll out with a rolling pin until about ⅛” thick. Cut out your cookies with cookie cutters of your choice and transfer cut outs to baking sheet. Re-roll the dough scraps and repeat.
Bake cookies for 10-12 minutes or until the edges just begin to brown. Let cookies cool on the baking sheet for at least 10 minutes until they’re firm enough to handle. Transfer them to a wire rack to cool completely.
In a small bowl, stir together powdered sugar and milk. It should be a thick paste when stirring around but looks smooth and glossy if you leave it undisturbed. Let the icing drizzle off the spoon - it should be thick enough for the drizzles to hold their shape for several seconds and then “melt” back into the icing.
Divide the icing into several smaller bowls and mix in gel food colouring into each bowl, depending on your designs. Note that adding a lot of gel colouring to the icing may make it thinner so add more powdered sugar as needed to maintain the thick consistency.
Transfer icing to small piping bags and cut off the tips to make a small opening. Cover any icing that isn’t being used so that it doesn’t dry out.
Pipe an outline of icing onto a cookie and fill it in with icing. Use a toothpick to move the icing aorund any gaps until it smooths out by itself. Repeat with all cookies and let them dry for at least 30 minutes to 1 hour before applying the second layer of your design.
Let iced cookies dry completely for 6-8 hours or overnight, preferably.
If applying gold leaf to cookies, dab a paintbrush in water and dab off the excess on a paper towel. Apply a very thin layer of water to the areas of the cookie where you want the gold leaf to stick.
Dry off the paintbrush and very gently dab onto the sheet of gold leaf to lift a small piece off. Touch the gold leaf to the wet areas to apply.