New York black and white cookies

Wash and dry the lemon. Finely grate the yellow peel without the white pith and weigh out 2 g.

Heat a conventional oven to 205 °C and line trays with baking paper. Beat the butter, white sugar, salt, baking powder, zest and 9.4 g vanilla. Break and beat the eggs, weigh the shell-free amount and add gradually. Gently alternate flour and milk, ending with flour.

Portion into discs about 76 mm across before baking, leaving about 6 cm between them as they spread. Bake for about 12 min per batch until set, with only slight colour at the edges. Cool for 30 min.

Mix 379 g icing sugar, 57 g corn syrup, 43 g hot water and 3.525 g vanilla. Spread over one half of each cooled cookie. Leave on a rack while preparing the chocolate.

Melt the chocolate gently over a water bath. In another bowl mix 315 g icing sugar, 57 g syrup, 57 g hot water and 3.525 g vanilla. Stir in the melted chocolate and cover the un-iced half. Let set on a rack for about 30 min before storing in a tin.