Put the butter in a large, microwave safe bowl and heat it until almost but not fully melted (if you wait for it to fully melt it can sputter and you’ll lose some of the fat needed in the dough).

Add the sugar, salt and vanilla and whisk very well - for at least a full minute. Then add the egg and whisk again, vigorously, until the mixture is shiny and light.

Sift in the cocoa, flour and baking soda then mix with a rubber spatula until there are no flour or cocoa bits visible (you might need to use your hands to get it fully mixed).

Cover the dough with plastic wrap to seal and set in the fridge for about an hour to chill.

Preheat the oven to 350 F. Line two greased cookie sheets with parchment paper.

Scoop the cookies using a disher (or an ice cream scoop) into mounds of about 1.5 tablespoons. Roll each dough ball between your palms to smooth it over then use the bottom of a small glass or a measuring cup (I use a ¼ cup) and press gently down to flatten slightly.

Bake the cookies for 9-10 minutes. Since this is a dark dough you won’t see any browning but the cookies will have flattened, spread and not have a ‘wet’ look.

If they’ve puffed up a bit you can gently press them down again with the measuring cup.

Let them cool fully before frosting.

Set the softened butter in a bowl and add the salt and vanilla, beat it to just incorporate the flavors.

Add the powdered sugar and cocoa and beat until combined. Add milk, a tablespoon at a time while beating, until the consistency is spreadable (but not thin - if it gets too thin you’ll need to add more powdered sugar).

Over a double boiler or in the microwave (in increments, stirring in between) melt the chocolate. Remove the chocolate from the heat before it’s fully melted then stir it until the rest of it melts (this way you avoid burning it). Set aside to cool.

Beat together the butter, sugar, salt and vanilla until smooth. Pour in the cooled chocolate and beat until just mixed.

Spoon or pipe the frosting on top of the cooled cookies. Leave them as is or decorate with flaked sea salt, or sprinkles or chocolate shavings.