Sift the flour, baking powder, salt and baking soda into a large bowl.
Note: The trick with biscuits is to touch them as little as possible. So work swiftly and do not overwork the ingredients.
Add the cold butter and then using either a pastry cutter or your fingers, cut the butter into the dry ingredients. Do not over-mix—there should still be a few big pieces of butter. The dough should look like coarse crumbs.
Make a well in the dry ingredients and pour in 3/4 cup of the milk. Using a wooden spoon, gently stir to form a loose/lumpy, sticky dough. As soon as the dough just comes together, stop mixing. There may be some dry and/or wet spots, this is okay. If the mixture is really dry, add another tbsp or so of milk—but generally 3/4 cup of milk is sufficient.
Next, lightly sprinkle your work surface with some flour and then turn the dough out onto it. Sprinkle with a bit more flour and then fold the dough over onto itself about 3 or 4 times. Again, do NOT over- mix the dough.
Gently form the dough into an approximately 1-inch thick disc. Using a floured biscuit cutter, cut the dough into rounds. Gently re-form the remaining dough and cut out the remaining biscuits. Depending on how thick the dough was formed, you should end up with about 8 biscuits.
Next, lightly spray a small baking tray with non-stick spray (or cover with a piece of parchment paper). Place the biscuits onto the tray in two rows. The two rows should touch, as this will help the biscuits rise more evenly in the oven.
Brush the tops of the biscuits with the melted butter and transfer to the preheated oven. Bake for 10 to 15 minutes or until the biscuits are lightly browned and a tester comes out clean. The texture of the inside should be light and soft.
Remove from the oven and place on a wire rack. Serve immediately while still very hot.