Start by bringing all the ingredients to room temperature if they were refrigerated. It's best to keep the refrigerated ingredients on the counter 30 minutes prior to baking.
In a medium sized bowl, mix sugar, olive oil, cocoa powder, apple sauce and pure vanilla extract using a hand mixer for 5-7 minutes till it is homogeneous.
Do not overmix. The mixture should not lighten too much as fluffy mixture would produce cakey cookies.
In another medium sized bowl, quickly whisk together dry ingredients whole wheat flour, baking powder and salt.
Add the dry mixture of the second bowl to wet mixture in 4-5 batches. Mix uniformly after each addition.
Do not over mix in this step. The ingredients should mix just enough to not have dry lumps. The dough would be a sticky at this time.
Cover the bowl with cling film and refrigerate the dough overnight. You can even do it for couple of hours if you are short on time. Do not skip this step. You can store refrigerated dough for upto 3 days.
On the day of baking, Preheat the oven to 350°F (180°C).
Line the cookie sheet with parchment paper.
Remove the bowl from refrigerator, using a melon scoop, scoop out the dough and shape into small balls using your hands.
You may need to lightly oil your palms before handling the dough. In between steps also keep lightly oiling your palms if required.
Dip these balls into a bowl of powdered sugar. Turn out to get it coated liberally.
If the dough gets sticky and not manageable then put the dough in the freezer for 10 minutes. It behaves well when cold.
Place the coated balls on prepared baking sheet.
Bake for 8-10 minutes in the preheated oven or just until the edges are slightly firm but center is still soft. I recommend a soft fudgy cookie than a firmer one.
For moist chewy cookies do not over bake or else cookies will dry out.
Leave to cool on tray for 5-10 minutes, then transfer to cooling rack to cool completely. Store in an airtight container at room temperature for 3-4 days. You can also store them in refrigerator in an air tight box for upto 10-15 days.