Preheat the oven to 200°C (392°F) and line a muffin pan with paper liners.
Scoop small spoonfuls of hazelnut spread onto a plate or into an ice cube tray and place in the freezer while preparing the batter.
Melt the butter gently in a saucepan or microwave and set aside to cool slightly.
In a large bowl, combine the flour, sugar, and baking powder until evenly mixed.
In another bowl, whisk together the eggs and milk until smooth.
Pour the wet mixture into the dry ingredients and mix until just combined.
Add the melted butter and stir until the batter is smooth and lump-free.
Fold in the chocolate chunks or chips, distributing them evenly throughout the batter.
Fill each muffin liner halfway with batter. Place a frozen portion of hazelnut spread in the center, then cover with more batter, leaving space for rising.
Bake for 20 minutes, or until the tops are golden and a toothpick inserted at the edge comes out clean.
Allow muffins to cool in the pan for 5 minutes before transferring to a wire rack.