Preheat the oven to 375ºF. Line a 12-cup muffin pan with cupcake liners and set aside.
Whisk together the dry ingredients: all-purpose flour, cocoa powder, salt, baking powder, baking soda, and sugar. Set aside.
Mix together the wet ingredients in a large mixing bowl: egg, cooled butter, vanilla, milk, and sour cream. Combine well.
Stir the dry ingredients into the wet ingredients and mix just until combined. Overmixing will make your muffins tough.
Add ½ cup of chocolate chips and fold gently into the batter.
Spoon about 2 tablespoons of batter into the bottom of each muffin liner in the muffin tin.
Place one rum chocolate truffle into the center of each muffin cavity and then cover with another scoop of batter.
Sprinkle some additional chocolate chips over the top of the batter, if desired.
Bake for approximately 18 minutes until the tops of the muffins are slightly puffed and appear dry on the top.
Cool muffins for about 10 minutes and then transfer to a cooling rack to finish cooling.
Truffle centers will remain soft and melty while muffins are warm. You can reheat muffins in the microwave for 10-15 seconds to remelt the truffle center.
Reheat leftover ganache in the microwave until fluid. Spoon ganache over top of muffin.
Sprinkle gold sprinkles on top.