In a mixing bowl, sift the whole wheat flour and baking soda. Add powdered oats, jaggery powder, and salt. Whisk well to incorporate everything well.
Add butter, work the butter into the flour with your fingertips to resemble breadcrumbs.
Add milk, a tablespoon at a time and knead until you have a dough. You may need more or less of milk, so add it gradually. Do not overwork the dough. Just knead until the dough comes together.
Flatten the dough into a disc and transfer it to a cling wrap. Refrigerate for about 15 minutes.
Preheat the oven to 350 degrees F/ 180 degrees C. Transfer the disc to your work surface. Place it between two parchment papers and roll out to 1/4 inch thickness. If it crumbles, accumulate it and roll out. Use of parchment paper will help you roll it out nicely.
Use a cutter to cut into desired shapes.
Transfer to a baking tray lined with Silpat/parchment paper. Gather the scraps, form a disc, and repeat the same procedure of rolling out and cutting it out until all the dough is used up.
Use a skewer/fork to poke holes all over the cookies.
Bake for 15 minutes, until the cookies are a light golden in color. Check after 10 minutes of baking, as the time taken to bake will depend upon the thickness of the cookies, if they are thinner, they will be done around 10 -12 minutes. I baked in two batches, kept the other batch in the refrigerator while the first was baking.
Remove the tray from the oven. Let it cool for a minute on the tray, then transfer to a wire rack, and let it cool completely. They will become crisp and crunchy on cooling, transfer to an airtight container.