Add <quantity>250<unit>g</unit></quantity> of butter with <quantity>250<unit>g</unit></quantity> of chocolate chips to a pot over low heat. Stir until melted and combined

Transfer to a bowl and place in the refrigerator to cool down

Add <quantity>200<unit>ml</unit></quantity> of egg whites to a stand mixer with the whisk attachment. Whisk on medium-high speed until soft peaks are formed

Add <quantity>125<unit>g</unit></quantity> of sugar to the whites, <quantity>1<unit>tbsp</unit></quantity> at a time, while whisking for 3m until stiff and shiny. Reserve

Add <quantity>125<unit>g</unit></quantity> of sugar and <quantity>150<unit>ml</unit></quantity> of egg yolks to the stand mixer and whisk on medium-high speed until fluffy and pale yellow

Add the chocolate and butter mixture to the beaten yolks. Whisk on low speed to combine

Add the beaten egg whites to the chocolate cream in three parts, mixing after each addition, until you get a fluffy and airy cream

Preheat the oven to <temperature>170<unit>°C</unit></temperature>

Line the bottom of a <quantity>26<unit>cm</unit></quantity> springform cake pan with parchment paper. Grease the pan with baking spray

Pour <quantity>550<unit>g</unit></quantity> of the chocolate batter into the springform pan

Swirl the pan to evenly distribute the batter. Bake for 35m until a brown crust forms on the top and sides

Cover the remaining batter with cling film and place in the freezer to chill and firm

Remove the cake from the oven. It should be dry to the touch in the surface, but soft in the middle. Let it rest for at least 20m over the counter until completely cool

Top the cooled cake with the reserved batter and evenly spread it

Decorate with chocolate sprinkle

Place in the freezer for at least 2h to firm

Unmold the cake

Slice and serve. The gateau marcel is ready

You can enjoy as it is or top it with with ice cream and some fresh berries. Enjoy!