Put the sugar in a large jug followed by the mint (or use a pestle & mortar if you have one big enough).

Using the end of a rolling pin, pound the mint into the sugar so that it releases its oils.

Keep going until the mint and sugar form a sandy paste.

Pour 150ml of boiling water from a kettle into the jug and stir well.

Cover the jug, e.g. with a plate, and leave until the contents are completely cold (approx 2 hours).

Meanwhile

In hot, soapy water, wash the jug and also the bottle or jar you're going to use to store the cordial in. Dry the jug.

Put the oven on its lowest setting and place the bottle or jar on a baking tray inside.

Turn off the oven when the bottle or jar is hot, but leave inside until the cordial is ready.

Take a sieve (line it with cheesecloth or muslin if it's not very fine) and place it over a saucepan.

Tip in the contents of the jug and press down with a spoon to push all the liquid out and into the pan.

Over medium heat, stir until any undissolved sugar dissolves.

Turn up the heat and boil for 2 minutes.

Take off the heat and stir in the mint extract if using.

Transfer the cordial to the cleaned jug which will make it easier for you to pour it into the warm, sterilized bottle or jar.

Put on the lid and leave to go cold before storing in the fridge.