Combine the Aquavit, Vermouth, Habanero Shrub and Celery Shrub in a mixing glass half-filled with ice. Stir until chilled and diluted, about 20 seconds. Strain into a chilled rocks glass or coupe and garnish with a cocktail onion.
If you don't have bianco (aka blanc or sweet white) vermouth, Cocchi Americano, Manzanilla Sherry or even Lillet Blanc are great stand ins. A sweeter white wine and a few drops of Bittermens Scarborough Savory Herbal Bitters is also a great substitute for the bianco vermouth as well.