Mix together the flour, baking soda, and salt in a large bowl.
In a large mixing bowl, cream butter and sugar until light and fluffy. Mix in the eggs and almond extract.
Mix dry ingredients a little at a time to butter mixture. Mix until flour is incorporated, and the dough comes together.
The dough needs to be chilled. On the Kitchen Gifts web site, they recommend this great idea to help you start cutting out your cookies sooner than later. Take a spatula full of dough and put it in the middle of a piece of parchment paper. Cover the dough with the same size parchment paper. Roll out the dough to 1/4″ thickness.
Place the dough on a baking sheet, cover with plastic, and let it chill in the refrigerator. Repeat the process until all the dough is used, and all the sheets of parchment are in the fridge. By the time you are done, the first sheet you put in should be done. If not, wait about 1/2 hour. They should be done by then. Take out the first batch, cut out, and start baking at 350 degrees for 8-10 minutes. The best thing is that you are not adding any additional flour to your cookies. If covered properly with plastic, these can stay in the fridge overnight.
In the mixing bowl from the mixer, pour in the warm water and the meringue powder. Mix it with a whisk until it is frothy and has thickened a bit, about 30 seconds.
Add the cream of tartar and whisk for another 30 seconds.
Pour all of the confectioners' sugar in the bowl and place the bowl on the mixer.
Use your paddle attachment on low speed and mix for 10 minutes. stop the mixer at least one time during the 10 minutes to push down the icing that gathers on the wall of the bowl. Your icing will get smooth, thick and creamy.
Place in a sealed container until you are ready to use.
Mix some of the icing with brown color until it is your desired color. Add water to the icing, a little bit at a time, until it is the consistency that will allow you to outline the cookie and fill in the acorn. A good way to gauge this is to pull a spoon through the icing and count to ten. During the ten seconds the icing should go back together where it was pulled apart.
Place the icing in a decorating bag using a Wilton #2 tip. Outline the acorn. Fill in the bottom half of the acorn. Fill in the top part of the acorn.
Decorate the tops of the acorn with brown sprinkles, chopped cashews, and chocolate Heath pieces. Let dry and enjoy!