Black and white cookies

Whisk the two cups of all-purpose flour with half a teaspoon each of baking soda and baking powder and the kosher salt.

Preheat the oven to 350.

Cream the room temperature butter with the cup of granulated sugar on medium high with a hand mixer until pale, light and fluffy, about four minutes with a hand mixer or two to three in a stand mixer with the paddle.

Beat in two teaspoons of vanilla extract.

Beat in the eggs one at a time; eggs at the same temperature as the butter emulsify smoothly instead of hardening it.

Alternate dry and wet, beginning and ending with dry: three additions of the flour mixture and two of the buttermilk, mixing on low only until a little flour remains so the gluten stays undeveloped.

Finish by folding with a spatula, scraping the sides and bottom so no part is left more buttery than the rest.

Portion the batter into two ounce pieces, about a quarter cup each, onto a plate or a parchment lined sheet tray.

Chill 20 to 25 minutes so the butter firms and the portions can be shaped.

Take six pieces at a time, roll each into a sphere with lightly floured hands, and space them out on a baking sheet; keep the rest covered in the fridge.

Flatten each slightly to about three quarters of an inch tall and bake on the centre rack until the centres are matte and springy and the cookies are still very pale, with only a little gold at the edge.

While they are still very hot, set a large circular cutter over each cookie and move it in small circles to make it perfectly round.

Cool them on the baking sheet long enough that they will not groove, then turn them over onto a rack to cool fully.

Icing: put the confectioner's sugar in a bowl with two tablespoons of milk, two tablespoons of corn syrup, a teaspoon of vanilla extract, a pinch of salt and two tablespoons of boiling water.

Whisk gently at first until incorporated, to a thick but pourable, ribbony icing that will settle and dry smooth.

Ice half of each cookie: draw the icing up with a small offset spatula, let it run into a line down the middle, then work it out to the edge and fill in to an opaque layer.

Adjust with a little more powdered sugar if the icing runs off the edge, or tap water half a teaspoon at a time if it is too thick.

Stir two tablespoons of unsweetened cocoa powder into the remaining vanilla icing, adding a little extra water because the cocoa tightens the texture.

Ice the second half of each cookie with the chocolate icing, following the line already laid and handling them carefully so the vanilla finish does not crack; scrape off any drips.

Let the icing set. They keep in an airtight container at room temperature but are best the day they are made.