Preheat the oven to 350°F (180°C) and line a baking tray with parchment. For air fryer, preheat to 320°F (160°C).
Whisk the melted (and cooled) butter with the powdered sugar in a mixing bowl until smooth. The butter should be liquid but not hot.
Crush the whole cumin seeds fresh in a mortar and pestle. Stir into the butter mixture.
In a separate bowl, whisk together the flour, baking powder, and salt. Add to the butter mixture. Mix until crumbly.
Pour in the milk and bring the dough together into a firm log. If using whole wheat atta, add an extra 2 to 3 tablespoons of milk until the dough comes together.
Transfer the dough to a sheet of cling wrap. Shape into a log about 10 to 12 inches long and 1½ to 2 inches thick. Wrap tightly and refrigerate for at least 10 minutes (longer is better).
Slice the chilled log into rounds about ¼ inch thick. Arrange on the parchment-lined tray with space between each biscuit.
Oven: bake at 350°F for 12 to 15 minutes until the edges are lightly golden. Air fryer: bake at 320°F for 10 to 12 minutes.
Let the biscuits cool completely on the tray. They crisp as they cool. Store in an airtight container once fully cooled.