Preheat oven to 375⁰F/ 190⁰C. Grease and line two cookie sheets. Set aside.
Mix together in one bowl the first 3 dry ingredients the cornstarch, sugar and all-purpose flour. Set aside.
In separate bowl, softened the butter then add egg and vanilla beat until combined.
Mix together the dry and wet ingredients until it form smooth cookie dough.
Roll out cookie dough into ¼ inch in thickness then cut into rounds using a round cookie cutter.
Arrange 1-inch on the prepared cookie sheet. Bake in a preheated oven for 10 to 15 minutes or until done, but not browned. Let the cookies cool down then set aside for later use.
Prepare royal icing by mixing egg whites and lemon juice using a mixer until soft peaks form. Add confectioners’ sugar gradually and add 1 tablespoon of milk one at a time. Mix until fluffy, divide icing into 4 bowls then color each bowl with the needed color.
Place each colored icing in a piping bag and start decorating the cooled cookies with the earth design theme of your choice. Make sure to set the first application of the colored icing before applying the next, so as not to combine the two icing.