In a medium mixing bowl combine the flour, baking powder, and salt.

In a large bowl beat the butter until smooth. Gradually add in the sugar and continue mixing until fluffy.

Add in the egg and vanilla and beat until mixed well.

Slowly add in the flour mixture, mixing until just blended.

Turn the dough onto a floured surface and knead the dough into a ball and flatten into a disc shape. Cover with plastic wrap and refrigerate for at least 90 minutes or overnight.

When ready to bake the cookie preheat the oven to 375 degrees. Get out a large cookie sheet.

On a lightly floured surface roll the dough to 1/4 inch thick. Cut out the desired shapes and place on the baking sheet 2 inches apart.

Bake for 8-9 minutes or until the tops no longer look wet.

Remove from oven and cool for 2 minutes before transferring to a wire cooling rack to cool completely.

To make the royal icing combine all ingredients in a bowl and mix well. The mixture will be thick.

Divide the icing into 4 bowls and use gel food coloring to color each bowl.

Place a bit of icing into 4 zip top bags. Snip the end off of a bag and pipe an outline on one of the cookie shapes. Repeat with remaining icing.

At this point you will need to add a few drops of water to your icing to thin it out. The consistency you want is a slowly dripping icing that disappears into the bowl within about 10-12 seconds.

Place the sanding sugar in a shallow dish.

Flood the cookies one at a time with the thinned icing. Turn the cookie over and dip into the sanding sugar until the surface is covered in sprinkles. Do not press on the cookie too hard or the icing will run. If icing runs when you turn the cookie over it's too thin and you will want to add some powdered sugar.

Allow the cookies and icing to harden 12 hours on a cooling rack before storing them.