Preheat your oven to 350 degrees and line your muffin pan with 12 liners. Set aside.
In a medium bowl, add the flour, salt, and baking powder. Whisk together and set aside.
In another medium bowl (or the bowl of your stand mixer), add the butter and sugar and cream together on medium speed until light and fluffy.
Add the eggs, one at a time, mixing between each addition.
Add the vanilla, sour cream, and milk and mix until fully combined.
Pour in the flour mixture and mix until just combined.
Use a cookie scoop to fill each muffin liner about 1/3 full.
Use a small cookie scoop (or a teaspoon) to add a teaspoon of Nutella to each muffin tin and then gently create swirls with a toothpick.
Scoop the remaining batter evenly among the muffins.
Top with an additional teaspoon of Nutella to each and then gently swirl again.
Bake for 20 minutes or until just golden. Remove from oven and let cool on a wire rack.