Prep the pears. Wash, core, and chop the pears into small pieces.
You can peel them, but keeping the skins adds flavor and color. Aim for roughly 3 cups of chopped fruit.
Muddle with sugar. Combine pears and sugar in a nonreactive bowl (glass or stainless steel). Add a pinch of salt.
Mash lightly with a potato masher or the back of a spoon until the pears release some juice.
Add spices. Stir in crushed cardamom pods, sliced ginger, and the cinnamon stick. If using vanilla bean, add it now. If using vanilla extract, wait until the end.
Let it macerate. Cover and refrigerate for 12–24 hours.
Stir once or twice. The sugar will draw out the pear juices and create a fragrant syrup.
Strain the syrup. Place a fine-mesh strainer or cheesecloth over a clean bowl or large measuring cup. Strain the mixture, pressing gently to extract as much liquid as possible without forcing pulp through.
Add vinegar. Whisk in apple cider vinegar.
Taste and adjust: for a sharper shrub, add more vinegar; for sweeter, add a little more sugar and stir to dissolve. Remove whole spices. Stir in vanilla extract if you didn’t use a bean.
Bottle and rest. Pour into a clean glass bottle or jar.
Seal and refrigerate for at least 24 hours before using. This resting period helps the flavors meld and smooth out.
Serve. For a refreshing drink, mix 1–2 tablespoons shrub with 8 ounces chilled sparkling water over ice. Adjust to taste.
For cocktails, start with 1/2–1 ounce per drink.