In a medium-sized mixing bowl, beat butter until light and fluffy.
Mix in brown sugar and granulated sugar.
Mix in eggs one at a time until just combined.
In a separate mixing bowl, combine milk, dark rum, and vanilla.
In another mixing bowl, mix flour, baking powder, and salt.
Add flour mixture a little bit at a time alternately with rum mixture to the butter/sugar/eggs, mixing until just combined after each addition.
Grease an 8" x 8" baking pan and pour batter into the pan.
Bake for 50 minutes or until a toothpick inserted into the center of the cake comes out clean and the top begins to brown. I suggest slightly overcooking the cake. You don't want the cake to be too soft because you'll be adding a lot of liquid to it.
Passion Fruit Syrup Instructions
Fill a small saucepan on medium-high heat with passion fruit juice.
Bring to a boil and cook until it reduces by half (about 45 minutes).
While still on the heat, add sugar and stir until the sugar dissolves completely. The syrup will not be thick, but it will have a stronger and sweeter flavor than the juice.
Hurricane Rum Ball Instructions
In a medium-sized mixing bowl, mash up the rum cake (minus the one piece you ate) until you have quarter-sized crumbs.
Mix in powdered sugar, rum, passion fruit syrup, agave nectar, and lemon zest.
Cover and set aside for a few hours to let the liquid fully absorb into the cake.
Glaze and Assembly Instructions
In a small bowl, mix powdered sugar and passion fruit syrup.
Roll cake mixture into small balls, roll in glaze, and then roll in non-pareils.
Passion fruit syrup can be replaced by any fruit punch or hurricane mix. If you are using fruit punch or hurricane mix, do not follow the instructions for cooking it down and adding sugar; these beverages are already sweetened heavily.If you are using passion fruit juice to make passion fruit syrup, it's OK if the juice isn't 100% passion fruit, but it should be 100% juice. The one I used was pear juice and passion fruit juice. You will not use all of the syrup in the recipe - you can use leftover syrup to make drinks.These rum balls will work with any rum cake recipe.