Cut each plum in half, but do not pit. Or, leave the plums whole and prick holes all over the plums with a sterilized needle. Put the plums in a large crock or glass container. Add the sugar, vodka and brandy and stir to mix. Cover with cheesecloth or loose lid and store in a cool, dark place like a cabinet or closet. Let sit for 3 months, stirring once a month.
Strain the mixture through a wire mesh strainer or cheesecloth set over a large container. With the back of a wooden spoon, press the plums to extract as much of the liqueur as possible. Discard the plums. Restrain through clean cheesecloth. Store in sterilized bottles and cap with a cork or lid. The brandy can be served at this point, or kept to age for as much as 3 to 6 more months.
Makes about 1 quart