In a large mixing bowl, add butter and mix it with the sugar and eggs until fully combined.
Stir in the vanilla extract & Greek Yoghurt and mix until combined.
Add the flour and baking powder, and mix until combined with the help of a spatula.
Stir in the chocolate chips and chopped hazelnuts.
With the help of an ice cream scoop, arrange the batter evenly into a muffin tin lined with muffin cups.
Top each muffin with some extra chocolate chips and/or chopped hazelnuts and bake in an already heated oven at 350 F or 180 C degrees for about 20-22 minutes.
Let them cool slightly and serve for up to three days. Enjoy.