In a large mixing bowl, add your room temperature butter (or plant based butter) and sugar. Mix until light and fluffy.
Add egg, vanilla extract, mandarin orange juice and zest and mix well. Don't worry if your mixture starts to separate; it's normal.
In a separate large bowl mix together your dry ingredients; gluten-free flour blend with xanthan gum, corn starch, salt and baking powder and mix well.
Slowly with the mixer on low add the dry ingredients into the wet ingredients and mix well. Your cookie dough mixture will be thick and sticky.
Cover the orange cookie dough with plastic wrap and refrigerate for at least 2 hours or up to 3 days, if you are busy. Refrigeration prevents your cookies from spreading while baking.
Preheat oven to 350 degree F or 176 degree C.
Line your baking trays with parchment paper or baking mats to prevent sticking. Use a tablespoon to scoop a heaping tablespoon of orange cookie dough and drop it on the lined baking trays 2 to 3 inches apart. The cookies do not spread very much if you do not use real butter and refrigerate your dough.
Bake cookies for about 9 -12 minutes or until the edge of the cookies feel slightly firm but the middle of the cookie will still be slightly soft. These cookies do not turn golden brown on the top but the bottom of the cookie will be golden brown when cooked perfectly. 10 minutes was the perfect time for our oven but each oven varies a little. Do not wait until the tops of the cookie turn golden brown or they will be dry and not chewy.
Allow the orange drop cookies to cool for about 5 minutes on the baking sheet. Then, carefully use a spatula and move them to a wire rack to cool.
In a medium bowl add powdered sugar, mandarin orange juice and zest. Mix well. Drizzle the mandarin orange icing glaze over the cookies.
Allow the cookies to dry and enjoy. You can freeze these cookies so you can enjoy them through the holidays.