You will need a large kilner jar or a glass jar with an airtight seal. Collect enough greengages to fill the jar but still be just covered by the armagnac. Leave a little piece of stalk on each greengage. Prick the fruit with a needle 5 or 6 times and place in the jar.
Sweeten the armagnac with the sugar and pour in enough just to cover the greengages. Seal the jar and stand it in a ver