Preheat over to 400 degrees.
In a large bowl, cream butter and sugar with an electric mixer. Beat in eggs and vanilla. Add baking powder and flour, one cup at a time, mixing after each addition. The dough will be very stiff; blend last flour by hand if needed. ( If dough becomes too stiff and does not hold together in a ball, add water, a teaspoon at a time). Do not chill
Working with one cookie dough ball at a time, roll each out on a floured surface to 1/4" thick. Cut out star shapes.
Bake on ungreased cookie sheet on middle rack of oven; small and medium sized stars for 6-7 minutes, larger stars for 10-15 minutes or until light brown. Remove cookies from sheet immediately onto wire racks to cool.
To Make Royal Icing:
When making Royal Icing make sure the bowl and utensils are grease-free, since any trace of grease will cause it to break down. Royal icing dries quickly, so keep bowl covered with a damp cloth at all times.
3 level tablespoons Wilton Meringue Powder
4 cups sifted confectioner's sugar
6 tablespoons water*
Beat all the ingredients at low speed for 7-10 minutes (10 - 12 minutes at high speed for a portable mixer) until icing forms peaks. This icing can be stored in an airtight container and rewhipped before using. Makes 3 cups.
*For stiffer icing when using a heavy-duty mixer, add 1 tablespoon less water.
How to Assemble Tree:
You will need 2 of each size star to create the tree.
Add icing to piping bag and assemble cookies largest to smallest on doily covered cake stand. Place a dab or two of icing between each cookie as you stack them.
Place a dot of icing on each tip of the stars and add one red M&M candy to each. Let icing dry.
For top star, place one small star on wire rack. Water down Royal Icing and pour over one of the star. Let dry. Use Royal Icing to attach it to the top of the tree.
Sift confectioner's sugar over tree.