Preheat the oven to 350º, and line large, heavy baking sheets with parchment paper.

Place the sugars, oil, egg and vanilla in the bowl of a stand mixer, or in a large mixing bowl if using a hand mixer.

Beat until well combined - a couple minutes.

In a medium bowl, whisk together the flour, cocoa, baking powder and salt.

Beat dry ingredients into the sugar mixture just until combined.

Beat in the walnuts.

Press plastic wrap over the surface of the dough and refrigerate for several hours [or up to a week if you like]

Place about 1 cup 10X sugar in a flat bottomed bowl.

Portion onto the sheet pan with a medium cookie scoop [about 1 & 1/2 tablespoons each]

One by one, roll into balls, and then roll the balls in the 10X sugar, placing back on the baking sheet, a couple inches apart.

Bake for 8 minutes - they may not seem done, but they are. If you bake them any longer, you will lose the chewy texture.

Cool briefly on the baking sheets and then carefully remove them to a cooling rack.

Store at room temperature for up to a week, longer in the freezer.