Preheat oven to 350 degrees. Line a 9x13 baking dish with foil or parchment paper; leave some overhang to make removal easier. Spray foil with nonstick cooking spray. With an electric mixer, beat butter, sugar and brown sugar together until fluffy. Add in eggs and vanilla extract. Mix well. Lower speed and add flour, baking soda and salt. Mix until combined. Add 1 ½ cups M&M's and 1 cup mini chocolate chips and stir. Transfer cookie dough to prepared baking dish. Press remainder of M&M'S, mini chocolate chips and white chocolate chips into top of cookie dough. Bake 35 to 40 minutes on middle rack in oven. Let cool completely and cut.
For the Tri Colored Christmas Cookies:
Cream together shortening, butter and sugar until light and fluffy. Add egg, beating until well blended. Stir in sour cream, vanilla and almond extract, mixing well. Add flour, baking powder, soda and salt, beating well until dough forms into a ball. Add to cream mixture and beat well. Divide into three equal parts. Add red food coloring to one ball, mixing to a bright red color. To the second ball, add green food coloring and repeat process. Do not color third ball. Chill at least one hour. When ready to bake, tear off pieces of each colored dough ball and create a mosaic on a Silpat (silicone baking mat) or parchment paper. Roll out colored dough to ¼ inch thick. Using cookie cutters, cut out designs. Use up remaining dough scraps by combining them together, rolling out and cutting out more cookies. Bake for 9-10 minutes at 350 degrees. When slightly cooled, brush with icing and add decorative sprinkles. Keep cookies in an airtight container. Cookies can be frozen before they are iced.
For the Cookie Icing:
Stir powdered sugar, almond extract and water to desired consistency. If glaze is too thick, add more water. If too thin, add more powdered sugar. Glaze should be thin and runny enough for the decorative colors of the cookie to show through.