Pre-heat oven to 350°F (180°C) and grease a 10-inch (27 cm) loaf pan. Line the bottom with parchment. Grease the parchment too.
Mix ground almonds, cocoa, flour and salt in a small bowl. In a separate bigger bowl, whisk eggs, sugar, oil and sour cream.
Add the dry mixture into the wet one and stir till just combined.
Bake for 20-25 minutes and allow cool in the pan before turning out on the rack. When completely cooled, line the same loaf pan with cling film, covering the bottom and the edges of the pan. Place the cake back in the pan and leave to rest in the refrigerator for about 1 hour.
For the mousse:
Melt the chocolate in the microwave, stirring every 10 seconds, until just smooth. Set aside.
Whisk the egg yolks and pour in the melted chocolate, whisking continuously.
Prepare the double cream by combining the mascarpone and heavy cream together. Whisk with an electric hand mixer until soft peaks form. Fold the egg-chocolate mixture into the softly whipped cream.
In a separate bowl, beat the egg whites with an electric hand mixer until the whites start foaming. While still whisking the eggs, start adding the sugar, a teaspoon at a time, until the whites form stiff glossy peaks.
Quickly stir in one third of the meringue to the chocolate mixture. Add the rest of the meringue and the black pepper in and fold gently.
Pour this mousse on top of the cake and smooth out the top. Sprinkle the top with freshly cracked Timut black pepper. Freeze the mixture for 4 hours in the freezer. Transfer the cake to a serving plate and allow to defrost in the refrigerator for about 1 hour before serving, in order to allow the mousse to be softer.