Preheat the oven to 180°C/350F and grease a bundt tin. Set aside.
Place the softened butter, sugar and extract in a bowl and beat with an electric mixer for 2 minutes until light and fluffy.
Add in one egg and whip for a further 2 minutes. Continue with the remaining eggs, in the same manner.
Sift the flour, baking powder and soda into the mixture and beat for a further minute to combine well.
Place the white chocolate and nutmeg in a double boiler and melt on medium temperature, stirring often to ensure even melting.
Allow to rest and cool for 5 minutes, then pour into the cake batter and stir through to combine well.
In a separate bowl, slice the blackberries into thirds and stir into the yogurt.
Pour into the cake batter and fold the mixture through, ensuring it remains fluffy and the blackberries don’t break up too much.
Once well combined, pour into the prepared bundt tin and bake for 50 minutes or until a skewer comes out clean and lightly browned on top.
Remove from the oven and leave to cool for approximately 15 minutes, to the point where it has come loose from the tin. Turn out onto a cooling rack and allow to cool fully.
For the glaze, place the chocolate, butter and cream into a double boiler and melt until smooth. Add in the confectioner’s sugar, it should still be runny, but thick. Carefully and slowly spoon the glaze over the cake, ensuring even coverage over the entire cake.