Pre heat the oven to 180C. Grease two 8" round cake pans.

Sift all the dry ingredients together - buckwheat, cocoa, baking powder, baking soda, salt; in a large bowl.

In another large bowl, beat the eggs and brown sugar very well, using an electric mixer, until doubled in volume.

Add the oil and vanilla extract, mix well.

Reduce the speed to low, and add the flour mixture in three batches alternating with the yogurt, beginning and ending with flour mixture. Your batter will be thick.

Divide the batter equally between the prepared pans and bake for about 25 minutes or until a skewer inserted in the center comes out clean.

Let cool in the pans for 10-15 minutes. Turn the cakes out on a cooling rack. Let cool completely.

Bring the sugar and water to a boil. Let it cook for a couple minutes. Take it off the heat. Let it cool, then add rum (if using)

Combine butter and cream in a heavy bottomed pan. Heat them gently, until the butter melts. Take off the heat. Add the chocolate. Stir it in gently, until the mixture is smooth and shiny.

Whisk in the icing sugar. At this point, you can add in a couple tablespoons of cocoa powder, if you like a deeper chocolate taste - We do, so I did add the cocoa. Stir in rum, if using.

Let cool completely. It should get thick enough to spread easily.

Place one cake layer, right side down, on a platter. Brush over the simple syrup liberally. Spread a third of the frosting over the top. Carefully spread the jam on top of the frosting.

Brush some of the simple syrup on the second cake layer's bottom. Carefully place this layer on top of the first, right side up. Spread the remaining frosting all over the cake, covering the sides and the top.

Using a butter knife, make some swirl patterns on top and serve!