I made several of these this weekend.  I started with the basic formula that I posted before:

2 oz. bourbon
3/4 oz. vanilla vodka
1/2 oz. rich simple syrup
2 dashes mint bitters

Things I discovered:

Applejack, or in my case, 100 proof Captain Applejack Apple Brandy, can replace the whiskey.

The vodka and syrup can really be to taste; I was free pouring a couple of them and they still came out pretty tasty.  The trick was to make sure to have some ice in the glass to cut the burn (since I wasn’t actually mixing).

The bitters can be cut back nicely to just one dash.

Later this week I may experiment with this using Dr. McGillicuddy’s Vanilla Liqueur.