Lay the unwashed elderflower heads on a tray to let any bugs crawl out.

Remove any flower heads that look brown, snip off any larger, thicker green stems.

Put the kettle on to boil.

Put the elderflowers into a large, heatproof bowl. Grate the lemon and orange zest into it.

Squeeze the juice from the lemons and oranges and put it in a covered container in the fridge until the next day.

Pour 1½ litres of boiling water from the kettle over the elderflowers and zest.

Stir, then cover and leave overnight.

Sterilize your bottles:

Wash your bottles and lids in hot, soapy water then rinse and drain them.

Put the oven on its lowest setting and place the bottles on a baking tray inside (lay on their sides if necessary).

Turn off the oven when the bottles are hot, but leave inside until the cordial is ready.

Line a sieve with a piece of folded cheesecloth or muslin and place the sieve over a large saucepan.

Tip in the contents of the bowl. Press down with a spoon to push all the liquid out of the elderflowers and zest, then discard them.

Add the reserved lemon and orange juice to the liquid in the pan, along with all the sugar.

Put the saucepan over a gentle heat, stirring occasionally until the sugar is dissolved.

Turn up the heat and simmer the cordial for 3-5 minutes.

Carefully pour the elderflower cordial into the hot sterilized bottles: use a jug or funnel if necessary.

Put on the lids and leave to cool before storing in the fridge.