To crush candies easily, minus any peppermint shrapnel, place them in a resealable plastic bag and crush with a rolling pin, meat mallet, or the back of a large spoon.
Rye flour adds an earthy-nutty dimension and absorbs more molasses than all-purpose flour. The result is a cookie with the smoky caramel finish of rye whiskey.
Here, the word "perfect" refers not to the quality of the classic cocktail (though we do love this version), but to the equal amounts of sweet and dry vermouth used to make it.