Please make sure the butter and eggs are at room temperature. Cream butter and sugar using a paddle attachment if you are using a stand mixer. Cream until they are fluffy and pale in color. Add egg and vanilla extract and continue to mix for few seconds. Sift in the dry ingredients and continue to cream just until combined. Do not overmix. There may be still some dry bits of flour on the side of the bowl. Just use a spatula to fold them into the cookie dough
The dough is soft and sticky at this point. Scrape the dough using a spatula on top of a cling wrap and wrap with a cling wrap while roughly shape it into a disc. Chill in the fridge for at least 2 hours or up to 24 hours
Shaping:
The dough is easier to handle after being chilled. Divide the cookie dough into 10 equal pieces. You can weigh the dough and divide into 10. Roll them into round balls and flatten into about 1/2-inch thick and about 3-inches in diameter. Place them on a large baking sheet lined with parchment paper, about 1/2-1 inch apart. They won't spread much
Baking:
Preheat the oven to 375 F (190 C) for at least 10 minutes. Place the baking sheet on the middle rack and bake for 8-9 minutes. DO NOT overbake the cookies. They will appear still very soft when they are just out from the oven. Let the cookies cool down on the baking sheet. Don't try to move them when they are still soft
Prepare frosting:
You may not use up all the buttercream frosting, depending on how much you want to put on the cookies. They can be kept frozen and thaw at room temperature before using. They are really good that my kids who usually scrape off frosting from sugar cookies, asked for more frosting :) If you have sweet tooth tough, you may find this frosting not sweet enough, in that case, feel free to increase the amount of icing sugar to your preference
Place a softened room temperature butter in a mixing bowl along with the sugar. Whip on medium speed (speed 6 on KA) until the mixture is pale and creamy. Add condensed milk and whip again until it's fully combined. The buttercream texture should be smooth, creamy, and easily spreadable
You can add few drops of pandan essence on half of the butter cream and few drops of ube extract on the other half.
Assembling:
You can transfer the buttercream to piping bag and pipe the frosting on top for a neat look or just spread it on top of the cookies. Decorate with sprinkles if you wish