When it's too cold for mint to be growing in the garden, make a kumquat martini by swapping out the creme de menthe for orange liqueur and subbing a few sliced kumquats for the mint.
Fill a large cocktail shaker with ice. Add coffee liqueur, vodka, creme de menthe, and mint sprigs. Add espresso. If necessary, add more ice to fill shaker. Shake aggressively until the outside of the shaker is frosty. Strain into chilled martini glasses and garnish with additional mint.