Mix cream butter and brown sugar on high speed in a sizable bowl with a hand mixer or an electric mixer fitted with a paddle attachment until creamy.
Mix well after adding the vanilla extract.
Take the bowl out of the mixer stand, if using, and then sift the flour and baking powder into the butter mixture.
Take the bowl back to the mixer stand and incorporate the dry ingredients into the mixture of butter until it is well mixed. The dough will be quite delicate.
Add milk and mix slowly until the dough comes together. Keep beating till a smooth dough is formed.
Onto a piece of plastic wrap, turn the dough out. Wrap firmly and cut out a log that is approximately 1 1/2 x 2 1/2 inches in size.
For at least three hours or all day, keep it in the fridge.
Preheat the oven to 350 F. Use silicone baking mats or parchment paper to line a cookie sheet.
Slice the dough log into 1/4-inch-thick pieces. Be sure to leave enough space around the cookies since they’ll expand.
Bake the cookies for 12 to 15 minutes, until they are golden brown.
Before transferring the cookies to the rack on a wire to cool, give them about 6 minutes to sit on the cookie sheet.