Preheat the oven to 420F.

In a large bowl combine flour, cocoa powder, baking powder, baking soda, espresso powder, salt, brown sugar, and milk powder. Whisk to combine and set aside.

In a separate bowl combine milk, vegetable oil, eggs, sour cream, and vanilla extract. Whisk to combine.

Add the wet ingredients into the center of the dry ingredients and whisk just until no dry pockets remain.

Gently fold in dark chocolate chunks and milk chocolate chunks with a rubber spatula.

Set the batter aside for 30 minutes to an hour to rest before baking.

While the batter rests, prep the filling.

Once the batter has rested, place muffin liners in every other cavity of the muffin pan.

Scoop the batter into the liners, filling each cup a little over ¾ of the way full.

Top each muffin with a sprinkle of reserved chocolate chunks before baking.

Bake for 6 minutes at 420F. When the timer beeps, drop the temp to 350F and bake for an additional 15-18 minutes.

Remove from baking pan and allow to cool completely before filling.

For the fudge filling, combine water, granulated sugar, cocoa powder, salt, and corn syrup in a sauce pot. Bring to a boil over medium heat.

Once boiling, drop the heat to medium-low and cook while stirring frequently until it thickens.

Add heavy cream and allow to boil for another 2 minutes.

Pour the mixture over dark chocolate chips and whisk to combine.

Once the muffins have cooled, fill them with the fudge filling using a piping bag or spoon.

Store leftover muffins in the freezer and thaw before serving.