Preheat the oven to 180°C.
Beat the margarine with the sugar and lemon zest until fluffy. Add the egg and mix well.
Add the flour, salt and baking powder and stir again.
Now add the buttermilk, little by little, while stirring.
Grease the baking tin with some oil, pour a base of dough into the tin, sprinkle the raspberries on top and pour the remaining dough over it.
Bake the cake for 35 to 40 minutes. You can check whether it is done by piercing it with a skewer. If no dough sticks to the stick anymore, the cake is done.
Let the cake cool for fifteen minutes before cutting it. Sprinkle with some icing sugar and some fresh raspberries and garnish with some mint leaves.