Mix together butter, sugar, and powdered sugar until light and fluffy.
Add egg, egg yolk, sour cream, vanilla and mix until combined.
Add in dry ingredients and mix well.
Split dough into 2 sections. Roll out dough to 1/4" or 3/8" between 2 pieces of parchment paper cut to the size of your baking sheets. Chill dough for 1 hour to overnight.
BAKE
Preheat oven to 375°. Remove the top sheet of parchment and use it to line your baking sheets. Cut the chilled dough into shapes, chill again for 5-10 minutes and bake for 10-12 minutes.
If your going to re-roll any scraps, you will need to follow the same process: re-roll scraps between parchment paper, chill for at least 1 hour, cut shapes and chill once cut for 5-10 minutes before baking.
ROYAL ICING
Place powdered sugar and meringue powder in mixer with paddle.
Add water, lemon juice, and vanilla and beat for 5-7 minutes until light and fluffy and stiff peaks form.
Be sure to use right away or cover as it will dry out quickly.
Portion out into 3 bowls and add 1/2 tsp. water and gel food color until desired consistency is reached.
Place your tipless piping bag into a tall glass with piping bag folded open around the rim of the glass. Pour colored frosting down into the piping bag. Cut a very small hole in the bottom of bag and pipe.
Let cookies dry on the table with a fan blowing on them for a few hours. Then lay in single layer in a large container, layer with parchment paper. Store in air-tight container or heat seal in individual bags.