In a big bowl, add the room temperature butter and sugar.
Mix them first using a spatula so that the sugar doesn't fly out,
Then switch to electric hand mixer / stand mixer. Mix it till its light, creamy and fluffy. Keep scrapping down the sides in between for even mixing.
Add heavy cream, vanilla extract, egg yolk and salt.
Mix it till they combine using the electric mixer or spatula. (preferably electric mixer)
Sift in the All-Purpose flour/ Cake flour and Cornstarch in 4 parts. Fold in the dry ingredients after adding each part using a spatula. Just mix it until all the dry ingredients are incorporated. Do not overmix.
Fill the dough in the piping bag. I used 4B piping tip. If your piping bag is too thin add one more bag over it.
Line a baking pan with parchment paper and pipe the cookies on the pan.
Bake it in the preheated oven for 15 - 18 mins. If you like soft cookies bake them for 15 mins. However these cookies traditionally have a crisp finish so its best to bake them up to 17 to 18 mins. Bake it as per your preference.
Let it cool completely.
Store it in a dry container.
Notes
Use proper measurement cups. Measure your flour correctly. Adding extra flour is not advisable. After filling the cup with flour level it off using knife.
Use good quality vanilla extract for enhanced flavor.
For crisper cookies, leave them in the oven after turning it off. Leave the oven door slightly open. This will dry out the cookies further.
Always use unsalted butter for baking. Each brand has different amount of salt in it. So its best to add the salt yourself.
If your dough turns too soft, put it in fridge for 15 min - 20 mins.
If you don't have piping tip, you can use ice cream scoop or table spoon to make the dough balls. If the dough is stiff enough you can even roll the dough with your hands to make balls and flatten then a little for even cooking.
You can always pipe the cookies and then chill then in fridge for an hour or more. Chilling the dough dehydrates the dough and they will hold a better shape in oven. The cookies spread less and butter takes longer to melt in the oven. In this case it will take 18 minutes to cook.
You can dip the cookies in chocolate ganache or candy melts and cover it with sprinkles. This makes it appealing for kids.
You can replace vanilla extract with almond extract for a different flavor. This works very well with a white chocolate dipped cookies with sprinkles.
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