Preheat oven to 400 degrees F. Place the hazelnuts on a sheet pan and roast for 6-8 minutes until lightly browned and fragrant. Cool slightly then rub the hazelnuts together between your palms to get as much skin off as possible.
Place in a high speed blender or food processor, and blend until the nuts turn to grainy powder.
Add the rest of the ingredients for the homemade Nutella, and blend until smooth and creamy. You can add a bit more oil to make it more creamy. Set aside.
Reduce the oven to 350 degrees F, and line a 12-cup muffin tin with liners. Spray with cooking spray.
In a large bowl, stir together almond flour, baking powder, and salt.
In a separate bowl, whisk together eggs, sugar, butter, and almond milk until smooth.
Pour wet ingredients over dry ingredients and stir until just combined.
Divide the batter among muffin cups.
Add 1 tablespoon of Nutella on top of each filled muffin cup. Use a small spoon or a toothpick to swirl the Nutella into the batter, moving the batter to the top to push the Nutella to the center.
Bake for 22-25 minutes until a toothpick inserted in the center comes out clean. Cool in the muffin pan for 10 minutes, then transfer to a wire rack to cool completely.