Step 1Place the vermouth in a nonreactive container with the ginger. Allow to infuse for 12 to 24 hours to desired taste before removing the ginger.
Step 2Fill a 12-ounce Collins-style glass four-fifths full of ice. Add 3 ounces of the ginger-infused vermouth, and finish with 3 to 4 ounces of tonic water. Garnish with the slice of lemon, and serve immediately.