Crush Oreo cookies and mix with melted butter.
Press the mixture into a 15 cm square pan.
Arrange 20 upright strawberries tightly over the crust.
Soak gelatin in cold water until softened.
Melt chocolate with cream over low heat.
Whisk in egg yolks and softened gelatin.
Let the mixture cool to room temperature.
Pour mousse over strawberries.
Refrigerate for at least 4 hours or overnight.
Loosen the cake with a warm towel and remove from the pan.
Dust with cocoa powder before serving.