Make the cookie dough:

• In a large bowl whisk together flour, baking powder, and kosher salt. Set aside.
• In another large bowl, melt the butter (I used the microwave) just until melted but not hot. Whisk in the sugar followed by the egg and vanilla. Whisk vigorously until the mixture is emulsified. You shouldn’t see any streaks of butter or egg.
• Slowly stir in the flour mixture.
• It does look like a dry dough, so I like to finish by hand, squeezing the dough together. This incorporates the flour faster without developing too much gluten.
• Roll your dough while it is at room temperature. Roll the dough to approximately ¼ inch. You will have the best results if rolled between two pieces of parchment, but you can also roll out on a lightly floured surface.
• Refrigerate the dough until chilled. This will only take 30 minutes, but I like to give it a full 2 hours or overnight to let the gluten relax.
• Cut & bake cookies:
• When you are ready to bake, preheat your oven to 325° F convection or 350° F conventional,  and line two baking sheets with parchment paper.
• Unstick the parchment from both sides of the dough, then cut shapes with a lightly floured cookie cutter. Chill the cookies before baking. It will only take about 20 minutes.
• Bake in preheated oven for 7-9 minutes or until the cookies look matte in the center and have a few small cracks. Some of the edges might have begun to brown. I bake all the same shapes on one sheet to ensure even baking.
• Cool completely before icing.

Make Royal Icing:

• In a large bowl or in the bowl of a stand mixer fitted with the whisk attachment, combine the dried egg whites and lemon juice. Whisk until soft peaks form.
• Add all the powdered sugar and whisk to combine.
• Separate the icing into different bowls and add food dye. Be sure to keep an eye on the consistency and stop adding if it gets too thin.
• For outlining using the ribbon test. The icing should cascade slowly off your spatula and remaining clearly visible on the surface for a few moments (about 5-6 seconds) before slowly disappearing.
• For flooding using the same ribbon test, the icing should cascade off your spatula and almost disappear instantly into the rest of the icing.

For the simple icing:

Simply whisk all the ingredients together, adding a little milk at a time until it flows from the whisk but briefly holds a line on top of the icing in the bowl.