This cookie is fun to make and fairly easy but one word of caution - you will need to keep it refrigerated in an airtight container once you put the frosting on it. Bring it out about 15 minutes before you want to serve it for the frosting to warm up. Maybe less if you are having a heatwave. We were having a heatwave when I made this cookie and my frosting was melting as I was piping it on!First, preheat the oven to 350 and make sure the rack is in the center position. Take a 9 inch, or as close as you have on hand, cake pan and spray with non-stick spray. In a large bowl, beat the butter and sugar together until creamy. Next, beat in the egg and vanilla extra until combined. Add in the baking soda, salt, Cream of Tatar and mix until combined. Slowly add in the flour until well combined. It will start to get a little thicker and stiffer. Gently fold in the patriotic M&Ms and sprinkles. Scoop into the cake pan and press down until even. Do not press it all the way out to the edges, the cookie will need room to expand. If you press the dough all the way to the edge it will rise up. You will end up with high edges and a thin center. Once the oven is preheated, place it on the center rack and bake for 18-23 minutes. If you use a larger pan, take some time off and keep checking it. If you used a smaller pan you'll want to add time. You'll know the cookie is done when the edges start to turn a golden brown, remove it from the oven and let it cool. The cookie will continue to cook some while it is cooling. When the cookie has completely cooled it's time to frost it! You can place the cookie on a cake board or a plate, whichever you prefer. Because it was so hot, we used canned frosting but you can also make a buttercream if you would like. Separate the frosting into 3 bowls. Dye one bowl blue, another red and leave the last one white. Lay a sheet of saran wrap on the counter. Scoop the frosting onto the saran wrap. Then roll it and twist the edges shut. Cut the edge of one side and slide into a pastry bag with a decorating tip. Pipe the frosting around the edge of the cookie. You can use any tip you like and make any design you like. Sprinkle a handful or so of M&Ms and patriotic sprinkles on the frosting. Store in a cool, dry place in an air-tight container until you are ready to enjoy.