The ratio of the two things is not fixed. but 5 parts Bourbon, 1 part Sweet Vermouth and a splash of Bitters
This is why there's Bourbon
OK, so this is simple again - like a Martini: Sweet Vermouth, Bourbon (just my way - Canadian or other whiskies lay as strong a claim and Angostura Bitters
The ratio of the two things is not fixed. but 5 parts Bourbon, 1 part Sweet Vermouth and a splash of Bitters