Preheat the oven to 350°F. Line an 8×8 baking pan with aluminium foil, and set aside.
In a medium bowl, beat together the butter and sugar until light and fluffy. Mix in the egg and vanilla until fully combined. Slowly mix in the flour until fully incorporated.
Press the mixture into the prepared baking pan. Place 9 spoonfuls of Nutella evenly spread out on the mixture. Take a knife and swirl the Nutella into the mixture to form swirls.
Place in preheated oven for 20-25 minutes, or until the top looks firm and golden.
Remove from oven allow to cool in the pan completely before removing to cut into squares.