Pulse instant oats in a mixer grinder to obtain a course powder. Then grind the brown sugar and lastly pulse the nuts.
Preheat oven @170 degrees Celsius.
In a mixing bowl, beat butter and powdered sugar till it is light and fluffy.
Add the oats flour, ragi flour (finger millet flour), whole wheat flour and powdered nuts.
Add baking soda and bring the dough together by adding milk (only as much as necessary to bind the dough).
Line a baking tray with parchment paper. Make smooth balls of 30 grams each and line them on the baking tray at least 2 inches apart. Keep any extra dough in the refrigerator.
Bake the cookies @170 degrees for 17-18 minutes. But as I always say, do keep a watch on your cookies. They will brown slightly. If needed, line your tray with a double layer of parchment paper to keep the bottom of the cookies from burning.
Take out the tray and let the cookies rest on the tray for 4-5 minutes. The cookies will still look soft.
Transfer cookies to a wire rack and let cool completely!
Store in an airtight container.