Place 6-9 tablespoons of Nutella on a tray with non stick paper and place in the freezer to set while you make the rest of the Nutella brownies.
Preheat the oven to 180°C (350°F) and line an 8"x8" baking pan with baking paper.
Place the butter, milk chocolate and Nutella in a saucepan and melt on a low heat.
In a bowl, beat the eggs, brown sugar and vanilla extract together until light and fluffy.
Pour in the chocolate mixture and beat.
Add in the flour and stir through.
Pour into the prepared baking pan and spread in an even layer.
Place the frozen pieces Nutella around the brownie mixture and lightly press them into the mixture.
Place in the oven for 20-25 minutes. The top and sides will be set and the middle should have a slight wobble. Insert a skewer and only light crumbs should be attached.