Add all ingredients in a mixing glass with ice and stir.
Strain into a rocks glass over fresh ice.
Express oil from a grapefruit peel over the drink and discard.
Garnish with a rosemary sprig. (Optional: Using a kitchen torch, flame the rosemary until it smokes and extinguish before serving.).
*Rosemary-infused Campari: In a large Mason jar, combine 12 oz Campari and 4 rosemary sprigs and seal. Let sit at room temperature for 24 hours, shaking occasionally. Strain out solids and keep in the refrigerator for up to one month.