Preheat the oven to 180 C / 350 F and line your baking tray with parchment paper.
In a large bowl combine the dry ingredients together - flour, baking powder, baking soda, cornstarch, and salt (except the sugar). Mix well and keep aside.
In another bowl cream the butter, sugar, and vanilla extract until it’s nice and creamy. Add in the egg and sour cream and beat until everything is combined well.
In small increments, add the dry mixture to the butter mixture. Mix until everything is combined well.
The dough should start taking shape. Make a rough thick disc out of it and refrigerate it covered with parchment paper for at least 1 hr.
Once the dough has been chilled, roll it to a 1/4 inch thickness and cut out the dough using a cookie cutter of about 2-3 inches in diameter.
Bake for 9-10 minutes. Cool completely before icing.
For the icing, beat the butter using an electric mixer. Slowly begin adding the sugar a little at a time and keep beating until the mixture holds shape and is creamy in texture. Add a bit of food color as desired, we used 1 drop.
Using a butter knife or icing spatula, apply icing onto the cookies and add your favorite sprinkles. You can also pipe the frosting for a neater look.
Video
Notes
Chill the dough for at least an hour otherwise it’ll be difficult to roll it.
Don’t overbake the cookies. Using both baking soda and baking powder along with cornstarch will make the cookies soft and fluffy just like the store-bought ones. So, don’t skip any of these ingredients.