Rick the sloes all over with a sharp needle.
Pour over the gin and stir in the sugar and almond essence.
Pour into a large airtight container, such as a corked storage jar, and fasten tightly.
Leave in a dark place for about 15 weeks to allow the mixture to infuse.
Shake the container occasionally.
Strain through a funnel lined with muslin or cheesecloth and pour into clean, dry bottles.
Seal the bottles and keep for at least 6 months before drinking.