To infuse the vodka. Place an entire ripe pineapple, peeled, cored, and sliced, in a glass container and cover with a bottle of vodka. Refrigerate pineapple for at least 48 hours. To assemble the drink. Pour 2 1/2 ounces of pineapple infused vodka and 3/4 ounces of Grand Marnier in cocktail shaker filled with ice. Shake vigorously and strain into a chilled martini glass. Garnish with orange peel.