Preheat the oven to 350 and generously butter your bundt pan.  Using your electric mixer, beat together the butter and sugar for a few minutes until the mixture has fluffed up, then add in the eggs, one at a time, beating well in between and scraping down the sides as needed.  Then beat in the zest – if using, and vanilla.

In a small bowl, whisk together the flour, baking powder and salt and then alternately add the flour mixture and buttermilk, starting and ending with the flour mixture, and beating well in between.  Make sure the sides have been scraped down and finish with a good beating.  Fold in the berries.

Scrape the batter into your prepared pan and bake for about 1 hour – the top should be a lovely golden brown and the cake inside the cracks should bounce back to a light touch.  Allow the cake to cool in the pan for about 10 minutes before turning out onto a platter to cool completely.  Sprinkle liberally with icing sugar before serving!