In a big bowl, beat butter and sugar till it is nice and fluffy. I would recommend using powdered brown sugar.
Add all the other ingredients excluding milk and mix gently. Do not knead. Use milk spoon by spoon to bind the dough. Once you can make small balls from the dough, do not add any milk further.
Line a baking tray with parchment paper. Make balls of approximately equal size and press them ever so gently. Arrange these on the tray at least 2 inches apart. You can keep the remaining dough, if any, in the refrigerator to be used later.
Bake the cookies in a preheated oven at approximately 170-180 degrees Celsius for 10-12 minutes. You will see the sides of the cookies turning brown. Do not overbake.
Remove the cookies from the oven. They will still be soft. Wait for a couple of minutes and then gently place them on a wire rack to cool.
Notes
You can skip dried blueberries if you don't have any.
If your dough is very soft, you can refrigerate it for some time.
You can use castor sugar instead of brown sugar.
You can bake for a few minutes extra to a get a crispier texture. Keep an eye on the oven though. The brookies can burn easily.