Kulhärdad Rom Espresso Martini

👩‍🍳 Gör så här

1. 1
   To brown the butter, melt 4 Tbsp. (½ stick) unsalted butter, cut into cubes, in a small saucepan over medium-low heat. Let sizzle, stirring to prevent milk solids from sticking on bottom of pan, about 3 minutes. Cook, watching carefully and continuing to stir as solids begin to brown, until solids are a light chestnut brown and aromatic, about 4 minutes more; keep in mind butter will continue to darken off heat. Remove from heat and let cool, about 10 minutes.
2. 2
   Add brown butter to a sealable freezer-safe container, such as a mason jar. Add 4 oz. dark rum and ½ tsp. vanilla extract. Mix well and seal container. Freeze overnight, then pour through a coffee filter to filter out congealed solids. Do Ahead: Fat-washed brown butter rum can be made 2 weeks ahead; cover and chill.
3. 3
   Combine 1½ oz. coffee liqueur, 1 oz. espresso, cooled, 1 oz. Fat-Washed Brown Butter Rum, and ½ oz. simple syrup (1:1) in a cocktail shaker. Fill with ice and shake until well chilled, about 10 seconds. Strain into a chilled cocktail glass. Garnish with a sprinkle of ground cinnamon.