Whisk both flours and the cocoa powder together. (If the cocoa is lumpy, sift the dry ingredients, then whisk to blend.)

Working with a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat the butter, both sugars and the salt together on medium speed until smooth, about 3 minutes. Drop in the yolks and beat for another minute, scraping the bowl as needed, then add the vanilla.

Turn the mixer off, add the dry ingredients all at once and mix on low speed until they are almost incorporated. This takes a minute more than you might think it should; at first the dough looks crumbly and then it starts to darken, moisten and come together. Mix in the kasha and chopped chocolate. Use a large flexible spatula to give the dough another few turns and mix in any loose ingredients. Turn the dough out and divide in half.

To make free-form cookies: Preheat the oven to 350 degrees. Shape each piece of dough into a disk. One at a time, place between pieces of parchment paper and roll out to a thickness of 1⁄4 inch. It’s the thickness, not the shape, that matters. (I usually go for a rough oval or round.) Peel away both pieces of paper from one piece of dough, then return the dough to one piece of paper and slide it onto a baking sheet (if you don’t loosen the bottom paper, the dough will curl during baking). Repeat with the second piece of dough. Sprinkle the dough with the sugar-salt mixture. Bake for 14 to 15 minutes, rotating the sheets top to bottom and front to back at the midway mark, or until the cookies are set — the edges will be more set than the center, which might still have a bit of give when gently prodded. Slide each cookie slab, still on the parchment, onto the counter. Using a pizza wheel or a knife, cut the big cookie into as many cookies of whatever shape you like. I cut it into strips about 1 inch wide and then cut these diagonally so that I end up with diamond-shaped cookies. Slide the cookies, still on the paper, onto a rack to cool to room temperature.

To make slice-and-bake cookies: Roll each piece of dough into a log that’s 12 inches long. Wrap well and freeze for at least 1 hour, or refrigerate for at least 2 hours. When you’re ready to bake, preheat the oven to 350 degrees. Slice each log 1⁄3 inch thick and place the cookies about an inch apart on two baking sheets lined with parchment paper or silicone mats. Sprinkle with the sugar-salt mixture. Bake for 11 to 12 minutes, rotating the sheets top to bottom and front to back at the midway mark, until the cookies are firm around the edges and give slightly when pressed in the center. Transfer the cookies to racks to cool completely.

Storing: If you’d like, you can freeze the dough, either rolled out or shaped into logs, for up to 2 months; be certain to wrap it well. The logs can also be refrigerated for up to 3 days. The cookies can be baked (or sliced and baked) straight from the freezer; add a minute or two to the baking time. The cookies will keep covered at room temperature for about 4 days; they can be frozen, well wrapped, for up to 2 months.