First, make a blackberry puree by adding 1 cup blackberries (fresh or frozen), the juice of 1/2 lemon, and 1/4 cup simple syrup to a food processor or blender. Puree until smooth, then strain through a fine mesh sieve or chinoise.

For the cocktail, pack a shaker with ice.
Pour over the ice in equal parts:

Blackberry puree
Grey Goose Poire Vodka

Do not substitute vodka brands- other pear vodkas taste bad in this drink! Shake vigorously and strain into chilled martini glass. Garnish with a speared blackberry and sprig of mint.