8 tablespoons (1 stick) unsalted butter
1 3/4 cups brown sugar
1 teaspoon freshly grated nutmeg
1 teaspoon pure vanilla extract
1 (750-ml) bottle dark rum
3 cups boiling water
2 whole cinnamon sticks
In a large heavy-bottomed saucepan over medium heat, cook the butter until it begins to smell nutty and has turned a light-brown color. Watch the butter — you do not want to burn it or have brown or black flecks in it.
Add the brown sugar and nutmeg, and stir until the sugar has melted, about one minute. Remove from the heat.
Add the rum and vanilla to the saucepan. It will froth up, so be careful, pour slowly, and stir continuously. Add the boiling water and cinnamon sticks and stir.
Place pot back on the stovetop over very low heat just to keep warm. Use a ladle to serve in heatproof glass or mugs.