Preheat the oven at 175°C conventional oven.

Melt the butter. Pour the melted butter into a mixing bowl. Add the sugars and vanilla extract. Use a hand whisk and mix until combined, for about 30-60 seconds.

Add the egg and mix until just combined.

In a separate bowl mix together the flour, unsweetened cocoa powder, and salt.

Add it to the wet batter and gently mix the batter until just combined.

Pour the batter into a 16 cm silicon mold and smooth it out with the spatula.

Bake for about 12-14 min. Once baked let, it cool down. After it’s cooled down for 5-10 min, gently take it out of the silicone mold and let it cool down completely.

Pre-heat the oven at 200ºC conventional oven. Toast the hazelnuts for 5 min. Once toasted, let them cool down completely.

Make a dry caramel by slowly melting the sugar over low heat in a small pot until a nice amber color. Add the hazelnuts and fold them quickly together with a heat-proof silicone spatula. Be careful as it’s very warm. Spread it out on a silicone mat or baking paper. Let it cool down completely.

Once completely cooled down, use a strong blender, and blend it until smooth.

Place the brownie back into the same 16 cm (clean) silicone mold and pour the praliné on top of the brownie. Place it in the freezer to set, for a few hours.

Bloom the gelatin sheets in cold water.

Weigh out the greek yogurt and let it sit on the kitchen counter while preparing the Nutella and heavy cream.

Meanwhile, heat up 75g of the 250g heavy cream in a small pot on medium heat until it starts to slightly boil. Take the pot off the heat and add the gelatine sheet. Stir it in until the gelatine has dissolved.

Pour the heated heavy cream over the Nutella and with a spatula mix it together until cohesive. Take an emersion blender and blend it until smooth.

Add the Nutella mixture into the greek yogurt in 3 parts, to slowly combine the two mixtures.

Whip the remaining heavy cream until soft peaks. With the rubber spatula, gently fold together the whipped cream in 3 parts with the Nutella mixture until smooth and combined. Take your 18cm eclipse silicone mold and place a small board under the silicone mold to make it easier to move the mousse into the freezer. Pour the mousse into the mold.

Take the brownie out of the freezer and place the cake upside down, with the hazelnut praliné facing down into mousse, and place it in the center of the Nutella mousse.

Gently lift the mousse cake into the freezer for a minimum of 6 hours or preferable overnight.

Bloom the gelatin sheets in cold water.

Sift the cocoa powder over a bowl.

In a small pot, stir together water, sugar, and condensed milk and heat to a boil. Then take it off the heat and add the gelatin sheets, squeezing the excess water off the gelatin, and stir it in.

Hold the bowl at an angle and pour the hot liquid down the edge of the bowl to avoid creating air bubbles. With a rubber spatula gently stir the cocoa powder and liquid together until more cohesive. Then with an emersion blender, blend the glaze together until smooth. Pour the mirror glaze into a jug, holding the jug at an angle, to again avoid creating extra bubbles.

Place a piece of cling film over the glaze, so it touches the surface of the glaze and allows the glaze to cool until it reaches a temperature between 33-34ºC.

Prepare a baking tray with a piece of cling film. Place a cup upside down, for the cake to stand on.

Once the glaze has reached the wanted temperature, take the mousse cake out of the freezer and out of the mold and place it on the cup.

Pour the mirror glaze over the cake and let it drip off. Once set, remove any mirror glaze droplets hanging off the cake with a knife and lift the cake of the cup using two offset spatulas under the cake and gently lift it over to your serving dish. Place it in the fridge to defrost for 3-4 hours.

Temper the dark chocolate. Pour it into a small piping bag. Take the piping bag and cut a small hole. Pipe the chocolate on a few pieces of parchment paper in a wave movement. Let them firm up.

Once it ready, and you’re ready to serve, take the cake out of the fridge and gently add a few chocolate waves on the cake, as well as some halved and chopped hazelnuts and a little bit of edible gold dust. Save the other chocolate waves in an airtight container for decoration for other cakes.