Preheat your oven to 355 degrees F (160 degrees C) fan-forced.
In a bowl, add in Unsalted Butter (65 gram) and cream on high for about 30 second.
Add in Granulated Sugar (125 gram) and cream for another 30 second.
Add in Vanilla Extract (1 1/2 teaspoon) and cream for another 30 second.
Add in Oil (65 milliliter), beat on high until homogeneous, scrape down if needed
Add in Egg (3), one at a time on high.
Add in Milk (100 milliliter) and mix on high until combined.
Stir in All-Purpose Flour (200 gram), Unsweetened Cocoa Powder (6 tablespoon), Baking Powder (1 teaspoon), and Baking Soda (1 teaspoon) into the batter, mix on low until just combine.
Transfer about a tablespoon of batter onto your muffins pan with liners. Then, dollop Nutella® (24 teaspoon) spread using a teaspoon in the middle. Cover it with another tablespoon worth of cake batter.
Top up with some Chocolate Chips (to taste).
Bake it in the oven for 22 to 25 minutes.
Let it cool in the pan for at least 15 minutes transfer to a wire rack. Serve and enjoy!