Split the vanilla bean lengthwise and scrape out the seeds; reserve both seeds and pod.
Combine the water, granulated sugar, vanilla seeds, and the scraped pod in a small saucepan. Bring to a gentle simmer over medium heat, stirring until the sugar dissolves, 2–3 minutes.
Remove from heat, cover, and steep 15 minutes. Uncover, remove the pod, then stir in the vanilla extract and a pinch of salt. Let the syrup cool; transfer to a jar. (You will have extra syrup.)
Warm a mug with hot water, then discard the water. Brew a double shot (2 ounces) of espresso into the mug.
Steam the whole milk to 140–150°F with a silky microfoam. If you don’t have a steam wand, heat the milk to 150°F on the stovetop and vigorously whisk or shake in a jar until foamy.
Add 1.5 tablespoons of the vanilla syrup to the espresso and stir to combine.
Pour in the steamed milk, holding back the foam, then spoon a small layer of foam on top. Taste and add a little more syrup if desired.
Top with whipped cream for serving, if using. Serve immediately.