Preheat oven to 350°F (175°C). Grease a medium cake pan, or cover with a baking sheet.
In a medium to large bowl, blend well together all dry ingredients: the almond flour, the ground flaxseeds, the cocoa, the baking powder and a pinch of salt. Use a fork to mix.
In a separate, large bowl, beat the eggs - by hand or with an electric mixer. Add the water, slowly, while mixing. Add the softened butter and continue to mix. Add the vanilla and the sweetener and mix gently, just enough to make sure the ingredients are blended.
Introduce the dry mix into the wet mix, one spoon at a time, while mixing gently with a whisk.
Place the final mix into the pan - sprinkle with some hemp seeds if you like - and cook for about 30 minutes or until a toothpick comes out clean when checking the middle of the cake.
Let the cake cool on top of the stove before removing it from the pan and cutting it into slices or squares. Can be served with whipped cream or even with fresh cream poured over it, to increase the percentage of fats.