Clean and rinse the raspberries, then place them in a very large bowl.

Pour the lemon juice over the berries. Use a large spoon to stir the juice into the berries.

On the stovetop, heat 12 cups of water and 3 cups of sugar to a boil. Stir till the sugar dissolves. Remove from heat.

Pour the boiling water over the raspberries. Allow the water to cool for 1-2 hours to room temperature.

Cover the bowl with plastic wrap or a towel that you don't mind staining. Place in the refrigerator to steep for 24 hours.

Pour the cordial through a fine mesh sieve to strain.

Push gently on the solids with the back of a spoon, if you wish, to extract more juice. This will produce a slightly cloudy effect in the cordial, which will settle at the bottom of the storage bottle, but it won't change the flavor. If you'd prefer a clearer cordial, do not press down on the solids-- just strain them.

Once you've strained the juice from the berries, you will find that the leftover berries are mushy and quite sweet. Save them in the fridge, they are terrific served as a topping for ice cream.

This recipe makes a large batch of cordial, which will store very well in the refrigerator if you use a clean gallon jug. You can easily halve the recipe if you don't need quite so much cordial.

To serve, mix 1 part cordial with 1 part water or seltzer water. If you prefer a less sweet drink, dilute the cordial to taste. Serve cold.