Beat butter with stevia using an electric mixer until it gets smooth and fluffy. add sour cream and lemon juice and keep mixing. Start adding one by one egg.
Combine almond flour, coconut crumbs, baking soda, and psyllium. Start adding this mixture to butter and eggs mixture, spoon by spoon. Keep mixing.
When the batter is well mixed, add lemon zest and salt.
Preheat your oven to 160ºC (320ºF). Grease a 24 cm (9 inches) long bread mould with some butter and pour the batter in. Add 12 raspberries and push them with your finger so that they sink halfway into the batter.
Bake it in the oven for 45 minutes. Make sure you don't open the oven. Then reduce the heat to 120ºC (248ºF) and bake it for 15 more minutes.
While the bread is baking, prepare the syrup. Slice 1 lemon very thin, place it in a pot, add stevia, cinnamon stick, cloves, vanilla extract and water. Bring it to a boil and let it simmer for 5 minutes.
When the cake is baked, carefully, spoon by spoon, pour the syrup all around the edges and sprinkle in the middle.
For icing, beat mascarpone with lemon juice and sparkling mineral water. Add stevia and natural Rum aroma. Spread the icing all over the bread and decorate with raspberries and fresh mint leaves.
Chill for several hours before serving. Just before serving, you can sprinkle the raspberries and mint leaves with finely powdered coconut flour to mimic the icing sugar. There's no need to add more sweetener.