Sift together the flour, baking powder and salt then set aside.

In a mixing bowl and preferably using electric beaters, beat together the butter, sugar, vanilla, plus zest if using. Scrape down the sides of the bowl as necessary.

Beat in the egg along with a rounded tablespoon of the sifted flour until light and fluffy.

Beat in approximately HALF of the remaining flour.

FOLD in the remaining flour to create a soft dough.

Sprinkle a small amount of flour onto a piece of cling film and transfer the dough onto it. Sprinkle with a little more flour then wrap and put in the fridge to chill for 30 minutes (or 1 hour if the room was warm).

Divide the dough into four pieces, using scales for accuracy, then roll each piece into a rope approximately 20 cm long.

Tip: if the room is warm, work with one piece at a time and return the others to the fridge.

Cut each rope into 8 equal pieces, giving you 32 pieces in total.

Roll each piece into a cylinder approximately 4 cm long.

Tip: to get rounded ends and a uniform shape, roll each piece into a ball first then into a cylinder.

Note: if the room is warm you may wish to chill the cylinders in the fridge so they do not become too soft when handling.

Line one large or two regular baking trays with baking paper.

Put the milk in a small bowl and spread the sesame seeds in a wide shallow bowl or on a plate. Tip: you may wish to start with the smaller suggested amounts, adding more later if needed.

Take each biscuit, put into the bowl of milk and turn so all sides are coated.

Put into the sesame seeds and turn it around to completely coat.

Transfer to the prepared tray(s) leaving space between the biscuits as they will spread during baking.

Tip to reduce sticky hands: Keep one hand dry (for picking up the cylinders, dropping in the milk, turning in the seeds, and placing on the tray) and use the other for turning in the milk.

Preheat the oven to 180°C /160°C Fan /Gas 4 /350°F.

Transfer the trays to the oven and bake for 25 minutes or until the biscuits are a light golden brown.

Tip 1. If your oven cooks unevenly, turn the trays around partway through.

Tip 2. Cook for a further 5 minutes or increase the heat if you prefer a darker colour, but note that the biscuits may turn out harder. Watch carefully so they do not burn.

Transfer the biscuits to a cooling rack and leave until completely cold before storing in an airtight container.

Should keep for at least 1 week and up to a month.