For the biscuit crust: Heat the oven at 175 °C. Mix the blended biscuits, butter and sugar together until you get a homogeneous mixture. In a round cake tin, form a base core with the mixture and then bake for 10 minutes. Leave to cool completely.
For the chocolate mousse: Melt the butter and chocolate in a steam bowl, stirring constantly. Once melted, remove from the heat and whisk until smooth. Return to the heat and add the yolks, one at a time, stirring. Then set the mixture aside. In another bowl, beat the egg whites until soft snow is formed, gradually add half the sugar and beat until you get solid snow. Add the whites to the chocolate mixture and mix everything. Add half of the sweet cream (previously whipped) and mix until a homogeneous mixture is obtained. Put the chocolate mousse on the biscuit base at an even line. Refrigerate for a couple of hours. Before serving, beat the remaining sour cream and place on the chocolate tart. Decorate with chocolate chips.