Black and white cookies

Cream the softened butter into the sugar until very fluffy, in the narrowest bowl that will hold it so more of the mix stays against the beaters. It should look like mayonnaise.

Beat in the sour cream until the mixture looks like mayonnaise again.

Mix the eggs with the vanilla and almond extract and beat them in until smooth and fluffy.

Beat in the flour a little at a time.

Add the baking soda and baking powder with the second addition of flour, then the last of the flour.

Add a tiny pinch of salt, or half a teaspoon if the butter was unsalted.

Line two baking sheets with parchment and scoop about half a cup of batter per cookie, spaced far apart because they spread a lot.

Wet your hands with water and shape the mounds round without the batter sticking.

Bake at 350F, 180C, on convection; a little hotter without a fan.

At 18 minutes they were still squishy inside; at about 22 they were done. They should still look a little under-baked or they will dry out while the icing sets.

Cool completely and solidify before peeling them off the paper. The flat bottoms are the tops.

Stir the powdered sugar with the corn syrup and just enough water or milk to make a very thick but spreadable glaze; let lumps sit a few minutes and stir again rather than whisking.

Drizzle a straight line down the middle of a cookie and flood one half with plenty of icing; too little drags crumbs into it.

Let the white half set firm for about an hour.

Stir cocoa powder, a little extra liquid and more corn syrup into the remaining icing, then darken it with blue food colouring.

Drizzle the chocolate down the second half and flood it; the set white icing acts as a bank.

Let them set overnight; they do not taste right until the next day.

Snap off any excess icing, or cut a cleaner edge with a butter knife.