Preheat oven to 180°C

Halve plums and place cut-side up in a small roasting pan. Sprinkle with brown sugar and place in the oven for 40 minutes or until very tender

Strain plum mixture through a fine sieve, slightly pushing down with the back of a spoon to push through the syrup and puree. Discard solids. You should have about 125ml (1/2 cup) of plum syrup. Set aside to cool completely

Place ingredients into cocktail shaker with ice cubes and shake until chilled

Pour into martini glasses, and garnish with a plum slice. Enjoy responsibly