Preheat the oven to 350 degrees and position a rack in the center. Butter and flour your mini bundt cake forms and set them aside.
In a large bowl with an electric mixer cream together the butter and sugar then blend in the eggs, lemon zest and milk. In a small bowl combine the flour, baking powder and salt then add it to the lemon mixture and mix it until it's smooth. Make sure to scrape off any little bits of zest that stick to the beaters and reintroduce them to the mixture. Lastly, fold in the berries briefly and carefully making sure not to burst any.
Fill a large pastry bag without a tip with the batter and pipe it into the prepared mini bundt cake forms until each is filled about 3/4 of the way. Bake them for 15 - 20 minutes or until a toothpick inserted into the middle comes out clean and the tops are a light golden brown. Turn them out onto a cooling rack and enjoy!