Step 1

In a small bowl, whisk together the flour, baking powder and salt.

Step 2

In a medium bowl, beat together with an electric mixer the butter and sugar. Once light and fluffy, add the egg yolk and vanilla extract.

Step 3

Once well incorporated, sprinkle over half the flour mixture and beat gently until combined, then sprinkle over the rest. Beat until no streaks of flour remain, but be careful not to over-mix.

Step 4

Dust a clean counter top with flour, and dump half of the dough out onto it. Gather it into a ball and press it into a 1/2" thick round disk. Flour your rolling pin, then roll out the dough out big enough to cut out about 8-9 shapes. Place the shapes on a baking sheet lined with parchment paper or a silicone mat. Gather the dough scraps and re-roll to cut out 8-9 more shapes and place them on the cookie sheet. You should get roughly 16 cookies.

Step 5

Place the cookie sheet in the freezer for the minutes while you preheat the oven to 350.

Step 6

Once the oven is hot, bake the cookies for 10-12 minutes, until the edges of the cookies just start to turn brown. Let them sit on the sheet a few minutes before moving them a wire rack to cool completely.

Step 7

Once the cookies are cooled completely, make the royal icing: in a small bowl, combine the powdered sugar and lemon juice.

Step 8

Beat the egg white in a small bowl to loosen them, and then measure out 2 tablespoons of egg whites and add them to the bowl with the sugar.

Step 9

Whisk together the icing, starting slowly, and trust that the sugar will melt and it will become liquid. Resist the urge to add any more liquid to the bowl, and instead just keep whisk slowly.

Step 10

When the icing comes together, spoon a small amount onto each cookie, and use an off-set spatula to spread it almost to the edges.

Step 11

Let the royal icing harden completely on the cookies before proceeding.

Step 12

Using the green frosting tube, make a zig-zag Christmas tree shape in the center of a cookie. Immediately add the nonpareil sprinkles and press a star candy on top. Because the royal icing is already dry, the sprinkles will only stick to the Christmas tree shape. Repeat with all remaining cookies.