Beat the eggs with stevia at high speed. Add olive oil and keep beating. Now, add sour cream and beat for at least 3 minutes.
Mix 1/2 tsp baking soda with 1/2 tsp citric acid powder. Alternatively, use 1 tbsp of lemon juice. Add this to the batter and keep beating. Ad 2 tsp lemon zest and vanilla extract.
Mix all the dry ingredients, almond flour, coconut flour and psyllium. Add it to the batter spoon by spoon and make sure you mix it well.
Transfer 1/3 of the batter to another bowl and add 1 tbsp cacao powder. Mix well and set aside.
Prepare the Bundt cake mould and pour the light colour batter all the way. Now using a spoon add dark batter. Using a long wooden stick, make circular movements so that the two mixture create twirls and interesting shapes.
Bake at 160ºC (320ºF) for 50 minutes and then let it cool down in the oven.
Place all the ingredients in a deep saucepan and bring it to a boil. Let it simmer for 5 minutes and set aside.
When the cake is baked and cooled down a bit, take it out of the oven and slowly pour the syrup using a spoon. Let the cake "drink" the syrup slowly.
When the cake "drinks" all the syrup, gently remove it from the mould and sprinkle with powdered stevia sweetener.