All the ingredients should better be at room temperature.
- Lightly whisk the eggs with sugar and vanilla (or vanilla paste).
- Melt the butter, and cool it to room temperature.
- Add the sour cream, melted butter and baking soda to the egg mixture. Stir thoroughly.
- Divide the mass in two parts.
- Add the flour #1 to one part of the mass, and mix until smooth.
- Add the flour #2 and cocoa to the second part of the mass, and mix until smooth.
- Preheat the oven to 356F (180C).
- Grease a cake mold with butter (oil).
- Lay out alternately chocolate and light dough. In two or three layers. Maybe in a checkerboard pattern.
- At the end, draw a zigzag line along the dough with a knife or wooden stick.
- Sprinkle the cake dough with granola if desired.
- Bake the tea cake for about 50 minutes. Check for readiness with a wooden skewer.