Preheat oven to 170°C. Cream the butter and sugars for at least 5 minutes until the mixture becomes light and fluffy.
Add the egg and vanilla extract and beat well.
Add choc chips, flour, baking soda and baking powder. Beat on low speed until just combined (don't overwork the mixture or it can become tough).
Scoop a tablespoon of dough and flatten it into the palm of your hand. Add a dollop (1-2 tsp) of Nutella into the middle, then fold the cookie dough back up so that it seals and covers the Nutella completely.
Place the cookies on baking trays and sprinkle each one with sea salt.
Bake until cookies are golden around the edges, around 12-14 minutes.