Add rolled oats to a grinder and pulse to a flour consistency. (Measuring the oats so the cup is slightly heaping makes up for reduced volume after grinding.) In a large bowl combine whole wheat flour, ground oats, brown sugar, baking soda and salt. Mix together well.
Cut butter into pieces and add to the dry mixture. Cut in with a pastry blender, 2 knives or even your fingertips. Incorporate butter until evenly distributed and the mixture looks sandy.
Gradually add milk, starting with 2 tablespoons. Stir so the mixture begins to come together. (You must use your hands to start incorporating the milk to get an accurate feel for the dough.) Add only enough milk necessary to barely form a dough. You do not want the dough to be too sticky.
As soon as the dough comes together, cover with plastic wrap and chill in the refrigerator for 15 minutes.
Preheat oven to 350℉/177℃. Line 2 baking sheets with parchment paper. On a lightly floured surface, pat dough into a ball and sprinkle on a little more flour. Roll the dough to a thickness of around a ¼ inch. Using a 2½ inch round biscuit cutter, cut out rounds and place them evenly on the baking sheets. (You should get around 16-18 biscuits.)
Using the pointed end of a chopstick or the flat end of a wooden skewer, punch holes on the surface of each biscuit. Getting them in a consistent pattern will make them look uniform. Bake biscuits for 15-18 minutes or until the edges and bottoms look lightly golden.
Cool biscuits on baking sheets for 5-10 minutes before transferring to cooling rack. Store in an airtight container for up to 1 month.
Notes
If you don't want to add oats, use 1-1/2 cups of whole wheat flour.